Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-2.6-block.git] / include / uapi / linux / bpf.h

/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */
#ifndef _UAPI__LINUX_BPF_H__
#define _UAPI__LINUX_BPF_H__

#include <linux/types.h>
#include <linux/bpf_common.h>

/* Extended instruction set based on top of classic BPF */

/* instruction classes */
#define BPF_JMP32       0x06    /* jmp mode in word width */
#define BPF_ALU64       0x07    /* alu mode in double word width */

/* ld/ldx fields */
#define BPF_DW          0x18    /* double word (64-bit) */
#define BPF_XADD        0xc0    /* exclusive add */

/* alu/jmp fields */
#define BPF_MOV         0xb0    /* mov reg to reg */
#define BPF_ARSH        0xc0    /* sign extending arithmetic shift right */

/* change endianness of a register */
#define BPF_END         0xd0    /* flags for endianness conversion: */
#define BPF_TO_LE       0x00    /* convert to little-endian */
#define BPF_TO_BE       0x08    /* convert to big-endian */
#define BPF_FROM_LE     BPF_TO_LE
#define BPF_FROM_BE     BPF_TO_BE

/* jmp encodings */
#define BPF_JNE         0x50    /* jump != */
#define BPF_JLT         0xa0    /* LT is unsigned, '<' */
#define BPF_JLE         0xb0    /* LE is unsigned, '<=' */
#define BPF_JSGT        0x60    /* SGT is signed '>', GT in x86 */
#define BPF_JSGE        0x70    /* SGE is signed '>=', GE in x86 */
#define BPF_JSLT        0xc0    /* SLT is signed, '<' */
#define BPF_JSLE        0xd0    /* SLE is signed, '<=' */
#define BPF_CALL        0x80    /* function call */
#define BPF_EXIT        0x90    /* function return */

/* Register numbers */
enum {
        BPF_REG_0 = 0,
        BPF_REG_1,
        BPF_REG_2,
        BPF_REG_3,
        BPF_REG_4,
        BPF_REG_5,
        BPF_REG_6,
        BPF_REG_7,
        BPF_REG_8,
        BPF_REG_9,
        BPF_REG_10,
        __MAX_BPF_REG,
};

/* BPF has 10 general purpose 64-bit registers and stack frame. */
#define MAX_BPF_REG     __MAX_BPF_REG

struct bpf_insn {
        __u8    code;           /* opcode */
        __u8    dst_reg:4;      /* dest register */
        __u8    src_reg:4;      /* source register */
        __s16   off;            /* signed offset */
        __s32   imm;            /* signed immediate constant */
};

/* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */
struct bpf_lpm_trie_key {
        __u32   prefixlen;      /* up to 32 for AF_INET, 128 for AF_INET6 */
        __u8    data[0];        /* Arbitrary size */
};

struct bpf_cgroup_storage_key {
        __u64   cgroup_inode_id;        /* cgroup inode id */
        __u32   attach_type;            /* program attach type */
};

/* BPF syscall commands, see bpf(2) man-page for details. */
enum bpf_cmd {
        BPF_MAP_CREATE,
        BPF_MAP_LOOKUP_ELEM,
        BPF_MAP_UPDATE_ELEM,
        BPF_MAP_DELETE_ELEM,
        BPF_MAP_GET_NEXT_KEY,
        BPF_PROG_LOAD,
        BPF_OBJ_PIN,
        BPF_OBJ_GET,
        BPF_PROG_ATTACH,
        BPF_PROG_DETACH,
        BPF_PROG_TEST_RUN,
        BPF_PROG_GET_NEXT_ID,
        BPF_MAP_GET_NEXT_ID,
        BPF_PROG_GET_FD_BY_ID,
        BPF_MAP_GET_FD_BY_ID,
        BPF_OBJ_GET_INFO_BY_FD,
        BPF_PROG_QUERY,
        BPF_RAW_TRACEPOINT_OPEN,
        BPF_BTF_LOAD,
        BPF_BTF_GET_FD_BY_ID,
        BPF_TASK_FD_QUERY,
        BPF_MAP_LOOKUP_AND_DELETE_ELEM,
        BPF_MAP_FREEZE,
        BPF_BTF_GET_NEXT_ID,
};

enum bpf_map_type {
        BPF_MAP_TYPE_UNSPEC,
        BPF_MAP_TYPE_HASH,
        BPF_MAP_TYPE_ARRAY,
        BPF_MAP_TYPE_PROG_ARRAY,
        BPF_MAP_TYPE_PERF_EVENT_ARRAY,
        BPF_MAP_TYPE_PERCPU_HASH,
        BPF_MAP_TYPE_PERCPU_ARRAY,
        BPF_MAP_TYPE_STACK_TRACE,
        BPF_MAP_TYPE_CGROUP_ARRAY,
        BPF_MAP_TYPE_LRU_HASH,
        BPF_MAP_TYPE_LRU_PERCPU_HASH,
        BPF_MAP_TYPE_LPM_TRIE,
        BPF_MAP_TYPE_ARRAY_OF_MAPS,
        BPF_MAP_TYPE_HASH_OF_MAPS,
        BPF_MAP_TYPE_DEVMAP,
        BPF_MAP_TYPE_SOCKMAP,
        BPF_MAP_TYPE_CPUMAP,
        BPF_MAP_TYPE_XSKMAP,
        BPF_MAP_TYPE_SOCKHASH,
        BPF_MAP_TYPE_CGROUP_STORAGE,
        BPF_MAP_TYPE_REUSEPORT_SOCKARRAY,
        BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE,
        BPF_MAP_TYPE_QUEUE,
        BPF_MAP_TYPE_STACK,
        BPF_MAP_TYPE_SK_STORAGE,
        BPF_MAP_TYPE_DEVMAP_HASH,
};

/* Note that tracing related programs such as
 * BPF_PROG_TYPE_{KPROBE,TRACEPOINT,PERF_EVENT,RAW_TRACEPOINT}
 * are not subject to a stable API since kernel internal data
 * structures can change from release to release and may
 * therefore break existing tracing BPF programs. Tracing BPF
 * programs correspond to /a/ specific kernel which is to be
 * analyzed, and not /a/ specific kernel /and/ all future ones.
 */
enum bpf_prog_type {
        BPF_PROG_TYPE_UNSPEC,
        BPF_PROG_TYPE_SOCKET_FILTER,
        BPF_PROG_TYPE_KPROBE,
        BPF_PROG_TYPE_SCHED_CLS,
        BPF_PROG_TYPE_SCHED_ACT,
        BPF_PROG_TYPE_TRACEPOINT,
        BPF_PROG_TYPE_XDP,
        BPF_PROG_TYPE_PERF_EVENT,
        BPF_PROG_TYPE_CGROUP_SKB,
        BPF_PROG_TYPE_CGROUP_SOCK,
        BPF_PROG_TYPE_LWT_IN,
        BPF_PROG_TYPE_LWT_OUT,
        BPF_PROG_TYPE_LWT_XMIT,
        BPF_PROG_TYPE_SOCK_OPS,
        BPF_PROG_TYPE_SK_SKB,
        BPF_PROG_TYPE_CGROUP_DEVICE,
        BPF_PROG_TYPE_SK_MSG,
        BPF_PROG_TYPE_RAW_TRACEPOINT,
        BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
        BPF_PROG_TYPE_LWT_SEG6LOCAL,
        BPF_PROG_TYPE_LIRC_MODE2,
        BPF_PROG_TYPE_SK_REUSEPORT,
        BPF_PROG_TYPE_FLOW_DISSECTOR,
        BPF_PROG_TYPE_CGROUP_SYSCTL,
        BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE,
        BPF_PROG_TYPE_CGROUP_SOCKOPT,
        BPF_PROG_TYPE_TRACING,
};

enum bpf_attach_type {
        BPF_CGROUP_INET_INGRESS,
        BPF_CGROUP_INET_EGRESS,
        BPF_CGROUP_INET_SOCK_CREATE,
        BPF_CGROUP_SOCK_OPS,
        BPF_SK_SKB_STREAM_PARSER,
        BPF_SK_SKB_STREAM_VERDICT,
        BPF_CGROUP_DEVICE,
        BPF_SK_MSG_VERDICT,
        BPF_CGROUP_INET4_BIND,
        BPF_CGROUP_INET6_BIND,
        BPF_CGROUP_INET4_CONNECT,
        BPF_CGROUP_INET6_CONNECT,
        BPF_CGROUP_INET4_POST_BIND,
        BPF_CGROUP_INET6_POST_BIND,
        BPF_CGROUP_UDP4_SENDMSG,
        BPF_CGROUP_UDP6_SENDMSG,
        BPF_LIRC_MODE2,
        BPF_FLOW_DISSECTOR,
        BPF_CGROUP_SYSCTL,
        BPF_CGROUP_UDP4_RECVMSG,
        BPF_CGROUP_UDP6_RECVMSG,
        BPF_CGROUP_GETSOCKOPT,
        BPF_CGROUP_SETSOCKOPT,
        BPF_TRACE_RAW_TP,
        BPF_TRACE_FENTRY,
        BPF_TRACE_FEXIT,
        __MAX_BPF_ATTACH_TYPE
};

#define MAX_BPF_ATTACH_TYPE __MAX_BPF_ATTACH_TYPE

/* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
 *
 * NONE(default): No further bpf programs allowed in the subtree.
 *
 * BPF_F_ALLOW_OVERRIDE: If a sub-cgroup installs some bpf program,
 * the program in this cgroup yields to sub-cgroup program.
 *
 * BPF_F_ALLOW_MULTI: If a sub-cgroup installs some bpf program,
 * that cgroup program gets run in addition to the program in this cgroup.
 *
 * Only one program is allowed to be attached to a cgroup with
 * NONE or BPF_F_ALLOW_OVERRIDE flag.
 * Attaching another program on top of NONE or BPF_F_ALLOW_OVERRIDE will
 * release old program and attach the new one. Attach flags has to match.
 *
 * Multiple programs are allowed to be attached to a cgroup with
 * BPF_F_ALLOW_MULTI flag. They are executed in FIFO order
 * (those that were attached first, run first)
 * The programs of sub-cgroup are executed first, then programs of
 * this cgroup and then programs of parent cgroup.
 * When children program makes decision (like picking TCP CA or sock bind)
 * parent program has a chance to override it.
 *
 * A cgroup with MULTI or OVERRIDE flag allows any attach flags in sub-cgroups.
 * A cgroup with NONE doesn't allow any programs in sub-cgroups.
 * Ex1:
 * cgrp1 (MULTI progs A, B) ->
 *    cgrp2 (OVERRIDE prog C) ->
 *      cgrp3 (MULTI prog D) ->
 *        cgrp4 (OVERRIDE prog E) ->
 *          cgrp5 (NONE prog F)
 * the event in cgrp5 triggers execution of F,D,A,B in that order.
 * if prog F is detached, the execution is E,D,A,B
 * if prog F and D are detached, the execution is E,A,B
 * if prog F, E and D are detached, the execution is C,A,B
 *
 * All eligible programs are executed regardless of return code from
 * earlier programs.
 */
#define BPF_F_ALLOW_OVERRIDE    (1U << 0)
#define BPF_F_ALLOW_MULTI       (1U << 1)

/* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the
 * verifier will perform strict alignment checking as if the kernel
 * has been built with CONFIG_EFFICIENT_UNALIGNED_ACCESS not set,
 * and NET_IP_ALIGN defined to 2.
 */
#define BPF_F_STRICT_ALIGNMENT  (1U << 0)

/* If BPF_F_ANY_ALIGNMENT is used in BPF_PROF_LOAD command, the
 * verifier will allow any alignment whatsoever.  On platforms
 * with strict alignment requirements for loads ands stores (such
 * as sparc and mips) the verifier validates that all loads and
 * stores provably follow this requirement.  This flag turns that
 * checking and enforcement off.
 *
 * It is mostly used for testing when we want to validate the
 * context and memory access aspects of the verifier, but because
 * of an unaligned access the alignment check would trigger before
 * the one we are interested in.
 */
#define BPF_F_ANY_ALIGNMENT     (1U << 1)

/* BPF_F_TEST_RND_HI32 is used in BPF_PROG_LOAD command for testing purpose.
 * Verifier does sub-register def/use analysis and identifies instructions whose
 * def only matters for low 32-bit, high 32-bit is never referenced later
 * through implicit zero extension. Therefore verifier notifies JIT back-ends
 * that it is safe to ignore clearing high 32-bit for these instructions. This
 * saves some back-ends a lot of code-gen. However such optimization is not
 * necessary on some arches, for example x86_64, arm64 etc, whose JIT back-ends
 * hence hasn't used verifier's analysis result. But, we really want to have a
 * way to be able to verify the correctness of the described optimization on
 * x86_64 on which testsuites are frequently exercised.
 *
 * So, this flag is introduced. Once it is set, verifier will randomize high
 * 32-bit for those instructions who has been identified as safe to ignore them.
 * Then, if verifier is not doing correct analysis, such randomization will
 * regress tests to expose bugs.
 */
#define BPF_F_TEST_RND_HI32     (1U << 2)

/* The verifier internal test flag. Behavior is undefined */
#define BPF_F_TEST_STATE_FREQ   (1U << 3)

/* When BPF ldimm64's insn[0].src_reg != 0 then this can have
 * two extensions:
 *
 * insn[0].src_reg:  BPF_PSEUDO_MAP_FD   BPF_PSEUDO_MAP_VALUE
 * insn[0].imm:      map fd              map fd
 * insn[1].imm:      0                   offset into value
 * insn[0].off:      0                   0
 * insn[1].off:      0                   0
 * ldimm64 rewrite:  address of map      address of map[0]+offset
 * verifier type:    CONST_PTR_TO_MAP    PTR_TO_MAP_VALUE
 */
#define BPF_PSEUDO_MAP_FD       1
#define BPF_PSEUDO_MAP_VALUE    2

/* when bpf_call->src_reg == BPF_PSEUDO_CALL, bpf_call->imm == pc-relative
 * offset to another bpf function
 */
#define BPF_PSEUDO_CALL         1

/* flags for BPF_MAP_UPDATE_ELEM command */
#define BPF_ANY         0 /* create new element or update existing */
#define BPF_NOEXIST     1 /* create new element if it didn't exist */
#define BPF_EXIST       2 /* update existing element */
#define BPF_F_LOCK      4 /* spin_lock-ed map_lookup/map_update */

/* flags for BPF_MAP_CREATE command */
#define BPF_F_NO_PREALLOC       (1U << 0)
/* Instead of having one common LRU list in the
 * BPF_MAP_TYPE_LRU_[PERCPU_]HASH map, use a percpu LRU list
 * which can scale and perform better.
 * Note, the LRU nodes (including free nodes) cannot be moved
 * across different LRU lists.
 */
#define BPF_F_NO_COMMON_LRU     (1U << 1)
/* Specify numa node during map creation */
#define BPF_F_NUMA_NODE         (1U << 2)

#define BPF_OBJ_NAME_LEN 16U

/* Flags for accessing BPF object from syscall side. */
#define BPF_F_RDONLY            (1U << 3)
#define BPF_F_WRONLY            (1U << 4)

/* Flag for stack_map, store build_id+offset instead of pointer */
#define BPF_F_STACK_BUILD_ID    (1U << 5)

/* Zero-initialize hash function seed. This should only be used for testing. */
#define BPF_F_ZERO_SEED         (1U << 6)

/* Flags for accessing BPF object from program side. */
#define BPF_F_RDONLY_PROG       (1U << 7)
#define BPF_F_WRONLY_PROG       (1U << 8)

/* Clone map from listener for newly accepted socket */
#define BPF_F_CLONE             (1U << 9)

/* Enable memory-mapping BPF map */
#define BPF_F_MMAPABLE          (1U << 10)

/* flags for BPF_PROG_QUERY */
#define BPF_F_QUERY_EFFECTIVE   (1U << 0)

enum bpf_stack_build_id_status {
        /* user space need an empty entry to identify end of a trace */
        BPF_STACK_BUILD_ID_EMPTY = 0,
        /* with valid build_id and offset */
        BPF_STACK_BUILD_ID_VALID = 1,
        /* couldn't get build_id, fallback to ip */
        BPF_STACK_BUILD_ID_IP = 2,
};

#define BPF_BUILD_ID_SIZE 20
struct bpf_stack_build_id {
        __s32           status;
        unsigned char   build_id[BPF_BUILD_ID_SIZE];
        union {
                __u64   offset;
                __u64   ip;
        };
};

union bpf_attr {
        struct { /* anonymous struct used by BPF_MAP_CREATE command */
                __u32   map_type;       /* one of enum bpf_map_type */
                __u32   key_size;       /* size of key in bytes */
                __u32   value_size;     /* size of value in bytes */
                __u32   max_entries;    /* max number of entries in a map */
                __u32   map_flags;      /* BPF_MAP_CREATE related
                                         * flags defined above.
                                         */
                __u32   inner_map_fd;   /* fd pointing to the inner map */
                __u32   numa_node;      /* numa node (effective only if
                                         * BPF_F_NUMA_NODE is set).
                                         */
                char    map_name[BPF_OBJ_NAME_LEN];
                __u32   map_ifindex;    /* ifindex of netdev to create on */
                __u32   btf_fd;         /* fd pointing to a BTF type data */
                __u32   btf_key_type_id;        /* BTF type_id of the key */
                __u32   btf_value_type_id;      /* BTF type_id of the value */
        };

        struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */
                __u32           map_fd;
                __aligned_u64   key;
                union {
                        __aligned_u64 value;
                        __aligned_u64 next_key;
                };
                __u64           flags;
        };

        struct { /* anonymous struct used by BPF_PROG_LOAD command */
                __u32           prog_type;      /* one of enum bpf_prog_type */
                __u32           insn_cnt;
                __aligned_u64   insns;
                __aligned_u64   license;
                __u32           log_level;      /* verbosity level of verifier */
                __u32           log_size;       /* size of user buffer */
                __aligned_u64   log_buf;        /* user supplied buffer */
                __u32           kern_version;   /* not used */
                __u32           prog_flags;
                char            prog_name[BPF_OBJ_NAME_LEN];
                __u32           prog_ifindex;   /* ifindex of netdev to prep for */
                /* For some prog types expected attach type must be known at
                 * load time to verify attach type specific parts of prog
                 * (context accesses, allowed helpers, etc).
                 */
                __u32           expected_attach_type;
                __u32           prog_btf_fd;    /* fd pointing to BTF type data */
                __u32           func_info_rec_size;     /* userspace bpf_func_info size */
                __aligned_u64   func_info;      /* func info */
                __u32           func_info_cnt;  /* number of bpf_func_info records */
                __u32           line_info_rec_size;     /* userspace bpf_line_info size */
                __aligned_u64   line_info;      /* line info */
                __u32           line_info_cnt;  /* number of bpf_line_info records */
                __u32           attach_btf_id;  /* in-kernel BTF type id to attach to */
                __u32           attach_prog_fd; /* 0 to attach to vmlinux */
        };

        struct { /* anonymous struct used by BPF_OBJ_* commands */
                __aligned_u64   pathname;
                __u32           bpf_fd;
                __u32           file_flags;
        };

        struct { /* anonymous struct used by BPF_PROG_ATTACH/DETACH commands */
                __u32           target_fd;      /* container object to attach to */
                __u32           attach_bpf_fd;  /* eBPF program to attach */
                __u32           attach_type;
                __u32           attach_flags;
        };

        struct { /* anonymous struct used by BPF_PROG_TEST_RUN command */
                __u32           prog_fd;
                __u32           retval;
                __u32           data_size_in;   /* input: len of data_in */
                __u32           data_size_out;  /* input/output: len of data_out
                                                 *   returns ENOSPC if data_out
                                                 *   is too small.
                                                 */
                __aligned_u64   data_in;
                __aligned_u64   data_out;
                __u32           repeat;
                __u32           duration;
                __u32           ctx_size_in;    /* input: len of ctx_in */
                __u32           ctx_size_out;   /* input/output: len of ctx_out
                                                 *   returns ENOSPC if ctx_out
                                                 *   is too small.
                                                 */
                __aligned_u64   ctx_in;
                __aligned_u64   ctx_out;
        } test;

        struct { /* anonymous struct used by BPF_*_GET_*_ID */
                union {
                        __u32           start_id;
                        __u32           prog_id;
                        __u32           map_id;
                        __u32           btf_id;
                };
                __u32           next_id;
                __u32           open_flags;
        };

        struct { /* anonymous struct used by BPF_OBJ_GET_INFO_BY_FD */
                __u32           bpf_fd;
                __u32           info_len;
                __aligned_u64   info;
        } info;

        struct { /* anonymous struct used by BPF_PROG_QUERY command */
                __u32           target_fd;      /* container object to query */
                __u32           attach_type;
                __u32           query_flags;
                __u32           attach_flags;
                __aligned_u64   prog_ids;
                __u32           prog_cnt;
        } query;

        struct {
                __u64 name;
                __u32 prog_fd;
        } raw_tracepoint;

        struct { /* anonymous struct for BPF_BTF_LOAD */
                __aligned_u64   btf;
                __aligned_u64   btf_log_buf;
                __u32           btf_size;
                __u32           btf_log_size;
                __u32           btf_log_level;
        };

        struct {
                __u32           pid;            /* input: pid */
                __u32           fd;             /* input: fd */
                __u32           flags;          /* input: flags */
                __u32           buf_len;        /* input/output: buf len */
                __aligned_u64   buf;            /* input/output:
                                                 *   tp_name for tracepoint
                                                 *   symbol for kprobe
                                                 *   filename for uprobe
                                                 */
                __u32           prog_id;        /* output: prod_id */
                __u32           fd_type;        /* output: BPF_FD_TYPE_* */
                __u64           probe_offset;   /* output: probe_offset */
                __u64           probe_addr;     /* output: probe_addr */
        } task_fd_query;
} __attribute__((aligned(8)));

/* The description below is an attempt at providing documentation to eBPF
 * developers about the multiple available eBPF helper functions. It can be
 * parsed and used to produce a manual page. The workflow is the following,
 * and requires the rst2man utility:
 *
 *     $ ./scripts/bpf_helpers_doc.py \
 *             --filename include/uapi/linux/bpf.h > /tmp/bpf-helpers.rst
 *     $ rst2man /tmp/bpf-helpers.rst > /tmp/bpf-helpers.7
 *     $ man /tmp/bpf-helpers.7
 *
 * Note that in order to produce this external documentation, some RST
 * formatting is used in the descriptions to get "bold" and "italics" in
 * manual pages. Also note that the few trailing white spaces are
 * intentional, removing them would break paragraphs for rst2man.
 *
 * Start of BPF helper function descriptions:
 *
 * void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
 *      Description
 *              Perform a lookup in *map* for an entry associated to *key*.
 *      Return
 *              Map value associated to *key*, or **NULL** if no entry was
 *              found.
 *
 * int bpf_map_update_elem(struct bpf_map *map, const void *key, const void *value, u64 flags)
 *      Description
 *              Add or update the value of the entry associated to *key* in
 *              *map* with *value*. *flags* is one of:
 *
 *              **BPF_NOEXIST**
 *                      The entry for *key* must not exist in the map.
 *              **BPF_EXIST**
 *                      The entry for *key* must already exist in the map.
 *              **BPF_ANY**
 *                      No condition on the existence of the entry for *key*.
 *
 *              Flag value **BPF_NOEXIST** cannot be used for maps of types
 *              **BPF_MAP_TYPE_ARRAY** or **BPF_MAP_TYPE_PERCPU_ARRAY**  (all
 *              elements always exist), the helper would return an error.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_map_delete_elem(struct bpf_map *map, const void *key)
 *      Description
 *              Delete entry with *key* from *map*.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read(void *dst, u32 size, const void *unsafe_ptr)
 *      Description
 *              For tracing programs, safely attempt to read *size* bytes from
 *              kernel space address *unsafe_ptr* and store the data in *dst*.
 *
 *              Generally, use bpf_probe_read_user() or bpf_probe_read_kernel()
 *              instead.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * u64 bpf_ktime_get_ns(void)
 *      Description
 *              Return the time elapsed since system boot, in nanoseconds.
 *      Return
 *              Current *ktime*.
 *
 * int bpf_trace_printk(const char *fmt, u32 fmt_size, ...)
 *      Description
 *              This helper is a "printk()-like" facility for debugging. It
 *              prints a message defined by format *fmt* (of size *fmt_size*)
 *              to file *\/sys/kernel/debug/tracing/trace* from DebugFS, if
 *              available. It can take up to three additional **u64**
 *              arguments (as an eBPF helpers, the total number of arguments is
 *              limited to five).
 *
 *              Each time the helper is called, it appends a line to the trace.
 *              Lines are discarded while *\/sys/kernel/debug/tracing/trace* is
 *              open, use *\/sys/kernel/debug/tracing/trace_pipe* to avoid this.
 *              The format of the trace is customizable, and the exact output
 *              one will get depends on the options set in
 *              *\/sys/kernel/debug/tracing/trace_options* (see also the
 *              *README* file under the same directory). However, it usually
 *              defaults to something like:
 *
 *              ::
 *
 *                      telnet-470   [001] .N.. 419421.045894: 0x00000001: <formatted msg>
 *
 *              In the above:
 *
 *                      * ``telnet`` is the name of the current task.
 *                      * ``470`` is the PID of the current task.
 *                      * ``001`` is the CPU number on which the task is
 *                        running.
 *                      * In ``.N..``, each character refers to a set of
 *                        options (whether irqs are enabled, scheduling
 *                        options, whether hard/softirqs are running, level of
 *                        preempt_disabled respectively). **N** means that
 *                        **TIF_NEED_RESCHED** and **PREEMPT_NEED_RESCHED**
 *                        are set.
 *                      * ``419421.045894`` is a timestamp.
 *                      * ``0x00000001`` is a fake value used by BPF for the
 *                        instruction pointer register.
 *                      * ``<formatted msg>`` is the message formatted with
 *                        *fmt*.
 *
 *              The conversion specifiers supported by *fmt* are similar, but
 *              more limited than for printk(). They are **%d**, **%i**,
 *              **%u**, **%x**, **%ld**, **%li**, **%lu**, **%lx**, **%lld**,
 *              **%lli**, **%llu**, **%llx**, **%p**, **%s**. No modifier (size
 *              of field, padding with zeroes, etc.) is available, and the
 *              helper will return **-EINVAL** (but print nothing) if it
 *              encounters an unknown specifier.
 *
 *              Also, note that **bpf_trace_printk**\ () is slow, and should
 *              only be used for debugging purposes. For this reason, a notice
 *              bloc (spanning several lines) is printed to kernel logs and
 *              states that the helper should not be used "for production use"
 *              the first time this helper is used (or more precisely, when
 *              **trace_printk**\ () buffers are allocated). For passing values
 *              to user space, perf events should be preferred.
 *      Return
 *              The number of bytes written to the buffer, or a negative error
 *              in case of failure.
 *
 * u32 bpf_get_prandom_u32(void)
 *      Description
 *              Get a pseudo-random number.
 *
 *              From a security point of view, this helper uses its own
 *              pseudo-random internal state, and cannot be used to infer the
 *              seed of other random functions in the kernel. However, it is
 *              essential to note that the generator used by the helper is not
 *              cryptographically secure.
 *      Return
 *              A random 32-bit unsigned value.
 *
 * u32 bpf_get_smp_processor_id(void)
 *      Description
 *              Get the SMP (symmetric multiprocessing) processor id. Note that
 *              all programs run with preemption disabled, which means that the
 *              SMP processor id is stable during all the execution of the
 *              program.
 *      Return
 *              The SMP id of the processor running the program.
 *
 * int bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void *from, u32 len, u64 flags)
 *      Description
 *              Store *len* bytes from address *from* into the packet
 *              associated to *skb*, at *offset*. *flags* are a combination of
 *              **BPF_F_RECOMPUTE_CSUM** (automatically recompute the
 *              checksum for the packet after storing the bytes) and
 *              **BPF_F_INVALIDATE_HASH** (set *skb*\ **->hash**, *skb*\
 *              **->swhash** and *skb*\ **->l4hash** to 0).
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_l3_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64 to, u64 size)
 *      Description
 *              Recompute the layer 3 (e.g. IP) checksum for the packet
 *              associated to *skb*. Computation is incremental, so the helper
 *              must know the former value of the header field that was
 *              modified (*from*), the new value of this field (*to*), and the
 *              number of bytes (2 or 4) for this field, stored in *size*.
 *              Alternatively, it is possible to store the difference between
 *              the previous and the new values of the header field in *to*, by
 *              setting *from* and *size* to 0. For both methods, *offset*
 *              indicates the location of the IP checksum within the packet.
 *
 *              This helper works in combination with **bpf_csum_diff**\ (),
 *              which does not update the checksum in-place, but offers more
 *              flexibility and can handle sizes larger than 2 or 4 for the
 *              checksum to update.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_l4_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64 to, u64 flags)
 *      Description
 *              Recompute the layer 4 (e.g. TCP, UDP or ICMP) checksum for the
 *              packet associated to *skb*. Computation is incremental, so the
 *              helper must know the former value of the header field that was
 *              modified (*from*), the new value of this field (*to*), and the
 *              number of bytes (2 or 4) for this field, stored on the lowest
 *              four bits of *flags*. Alternatively, it is possible to store
 *              the difference between the previous and the new values of the
 *              header field in *to*, by setting *from* and the four lowest
 *              bits of *flags* to 0. For both methods, *offset* indicates the
 *              location of the IP checksum within the packet. In addition to
 *              the size of the field, *flags* can be added (bitwise OR) actual
 *              flags. With **BPF_F_MARK_MANGLED_0**, a null checksum is left
 *              untouched (unless **BPF_F_MARK_ENFORCE** is added as well), and
 *              for updates resulting in a null checksum the value is set to
 *              **CSUM_MANGLED_0** instead. Flag **BPF_F_PSEUDO_HDR** indicates
 *              the checksum is to be computed against a pseudo-header.
 *
 *              This helper works in combination with **bpf_csum_diff**\ (),
 *              which does not update the checksum in-place, but offers more
 *              flexibility and can handle sizes larger than 2 or 4 for the
 *              checksum to update.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_tail_call(void *ctx, struct bpf_map *prog_array_map, u32 index)
 *      Description
 *              This special helper is used to trigger a "tail call", or in
 *              other words, to jump into another eBPF program. The same stack
 *              frame is used (but values on stack and in registers for the
 *              caller are not accessible to the callee). This mechanism allows
 *              for program chaining, either for raising the maximum number of
 *              available eBPF instructions, or to execute given programs in
 *              conditional blocks. For security reasons, there is an upper
 *              limit to the number of successive tail calls that can be
 *              performed.
 *
 *              Upon call of this helper, the program attempts to jump into a
 *              program referenced at index *index* in *prog_array_map*, a
 *              special map of type **BPF_MAP_TYPE_PROG_ARRAY**, and passes
 *              *ctx*, a pointer to the context.
 *
 *              If the call succeeds, the kernel immediately runs the first
 *              instruction of the new program. This is not a function call,
 *              and it never returns to the previous program. If the call
 *              fails, then the helper has no effect, and the caller continues
 *              to run its subsequent instructions. A call can fail if the
 *              destination program for the jump does not exist (i.e. *index*
 *              is superior to the number of entries in *prog_array_map*), or
 *              if the maximum number of tail calls has been reached for this
 *              chain of programs. This limit is defined in the kernel by the
 *              macro **MAX_TAIL_CALL_CNT** (not accessible to user space),
 *              which is currently set to 32.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_clone_redirect(struct sk_buff *skb, u32 ifindex, u64 flags)
 *      Description
 *              Clone and redirect the packet associated to *skb* to another
 *              net device of index *ifindex*. Both ingress and egress
 *              interfaces can be used for redirection. The **BPF_F_INGRESS**
 *              value in *flags* is used to make the distinction (ingress path
 *              is selected if the flag is present, egress path otherwise).
 *              This is the only flag supported for now.
 *
 *              In comparison with **bpf_redirect**\ () helper,
 *              **bpf_clone_redirect**\ () has the associated cost of
 *              duplicating the packet buffer, but this can be executed out of
 *              the eBPF program. Conversely, **bpf_redirect**\ () is more
 *              efficient, but it is handled through an action code where the
 *              redirection happens only after the eBPF program has returned.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * u64 bpf_get_current_pid_tgid(void)
 *      Return
 *              A 64-bit integer containing the current tgid and pid, and
 *              created as such:
 *              *current_task*\ **->tgid << 32 \|**
 *              *current_task*\ **->pid**.
 *
 * u64 bpf_get_current_uid_gid(void)
 *      Return
 *              A 64-bit integer containing the current GID and UID, and
 *              created as such: *current_gid* **<< 32 \|** *current_uid*.
 *
 * int bpf_get_current_comm(void *buf, u32 size_of_buf)
 *      Description
 *              Copy the **comm** attribute of the current task into *buf* of
 *              *size_of_buf*. The **comm** attribute contains the name of
 *              the executable (excluding the path) for the current task. The
 *              *size_of_buf* must be strictly positive. On success, the
 *              helper makes sure that the *buf* is NUL-terminated. On failure,
 *              it is filled with zeroes.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * u32 bpf_get_cgroup_classid(struct sk_buff *skb)
 *      Description
 *              Retrieve the classid for the current task, i.e. for the net_cls
 *              cgroup to which *skb* belongs.
 *
 *              This helper can be used on TC egress path, but not on ingress.
 *
 *              The net_cls cgroup provides an interface to tag network packets
 *              based on a user-provided identifier for all traffic coming from
 *              the tasks belonging to the related cgroup. See also the related
 *              kernel documentation, available from the Linux sources in file
 *              *Documentation/admin-guide/cgroup-v1/net_cls.rst*.
 *
 *              The Linux kernel has two versions for cgroups: there are
 *              cgroups v1 and cgroups v2. Both are available to users, who can
 *              use a mixture of them, but note that the net_cls cgroup is for
 *              cgroup v1 only. This makes it incompatible with BPF programs
 *              run on cgroups, which is a cgroup-v2-only feature (a socket can
 *              only hold data for one version of cgroups at a time).
 *
 *              This helper is only available is the kernel was compiled with
 *              the **CONFIG_CGROUP_NET_CLASSID** configuration option set to
 *              "**y**" or to "**m**".
 *      Return
 *              The classid, or 0 for the default unconfigured classid.
 *
 * int bpf_skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)
 *      Description
 *              Push a *vlan_tci* (VLAN tag control information) of protocol
 *              *vlan_proto* to the packet associated to *skb*, then update
 *              the checksum. Note that if *vlan_proto* is different from
 *              **ETH_P_8021Q** and **ETH_P_8021AD**, it is considered to
 *              be **ETH_P_8021Q**.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_vlan_pop(struct sk_buff *skb)
 *      Description
 *              Pop a VLAN header from the packet associated to *skb*.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_get_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key *key, u32 size, u64 flags)
 *      Description
 *              Get tunnel metadata. This helper takes a pointer *key* to an
 *              empty **struct bpf_tunnel_key** of **size**, that will be
 *              filled with tunnel metadata for the packet associated to *skb*.
 *              The *flags* can be set to **BPF_F_TUNINFO_IPV6**, which
 *              indicates that the tunnel is based on IPv6 protocol instead of
 *              IPv4.
 *
 *              The **struct bpf_tunnel_key** is an object that generalizes the
 *              principal parameters used by various tunneling protocols into a
 *              single struct. This way, it can be used to easily make a
 *              decision based on the contents of the encapsulation header,
 *              "summarized" in this struct. In particular, it holds the IP
 *              address of the remote end (IPv4 or IPv6, depending on the case)
 *              in *key*\ **->remote_ipv4** or *key*\ **->remote_ipv6**. Also,
 *              this struct exposes the *key*\ **->tunnel_id**, which is
 *              generally mapped to a VNI (Virtual Network Identifier), making
 *              it programmable together with the **bpf_skb_set_tunnel_key**\
 *              () helper.
 *
 *              Let's imagine that the following code is part of a program
 *              attached to the TC ingress interface, on one end of a GRE
 *              tunnel, and is supposed to filter out all messages coming from
 *              remote ends with IPv4 address other than 10.0.0.1:
 *
 *              ::
 *
 *                      int ret;
 *                      struct bpf_tunnel_key key = {};
 *                      
 *                      ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
 *                      if (ret < 0)
 *                              return TC_ACT_SHOT;     // drop packet
 *                      
 *                      if (key.remote_ipv4 != 0x0a000001)
 *                              return TC_ACT_SHOT;     // drop packet
 *                      
 *                      return TC_ACT_OK;               // accept packet
 *
 *              This interface can also be used with all encapsulation devices
 *              that can operate in "collect metadata" mode: instead of having
 *              one network device per specific configuration, the "collect
 *              metadata" mode only requires a single device where the
 *              configuration can be extracted from this helper.
 *
 *              This can be used together with various tunnels such as VXLan,
 *              Geneve, GRE or IP in IP (IPIP).
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_set_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key *key, u32 size, u64 flags)
 *      Description
 *              Populate tunnel metadata for packet associated to *skb.* The
 *              tunnel metadata is set to the contents of *key*, of *size*. The
 *              *flags* can be set to a combination of the following values:
 *
 *              **BPF_F_TUNINFO_IPV6**
 *                      Indicate that the tunnel is based on IPv6 protocol
 *                      instead of IPv4.
 *              **BPF_F_ZERO_CSUM_TX**
 *                      For IPv4 packets, add a flag to tunnel metadata
 *                      indicating that checksum computation should be skipped
 *                      and checksum set to zeroes.
 *              **BPF_F_DONT_FRAGMENT**
 *                      Add a flag to tunnel metadata indicating that the
 *                      packet should not be fragmented.
 *              **BPF_F_SEQ_NUMBER**
 *                      Add a flag to tunnel metadata indicating that a
 *                      sequence number should be added to tunnel header before
 *                      sending the packet. This flag was added for GRE
 *                      encapsulation, but might be used with other protocols
 *                      as well in the future.
 *
 *              Here is a typical usage on the transmit path:
 *
 *              ::
 *
 *                      struct bpf_tunnel_key key;
 *                           populate key ...
 *                      bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
 *                      bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);
 *
 *              See also the description of the **bpf_skb_get_tunnel_key**\ ()
 *              helper for additional information.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * u64 bpf_perf_event_read(struct bpf_map *map, u64 flags)
 *      Description
 *              Read the value of a perf event counter. This helper relies on a
 *              *map* of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The nature of
 *              the perf event counter is selected when *map* is updated with
 *              perf event file descriptors. The *map* is an array whose size
 *              is the number of available CPUs, and each cell contains a value
 *              relative to one CPU. The value to retrieve is indicated by
 *              *flags*, that contains the index of the CPU to look up, masked
 *              with **BPF_F_INDEX_MASK**. Alternatively, *flags* can be set to
 *              **BPF_F_CURRENT_CPU** to indicate that the value for the
 *              current CPU should be retrieved.
 *
 *              Note that before Linux 4.13, only hardware perf event can be
 *              retrieved.
 *
 *              Also, be aware that the newer helper
 *              **bpf_perf_event_read_value**\ () is recommended over
 *              **bpf_perf_event_read**\ () in general. The latter has some ABI
 *              quirks where error and counter value are used as a return code
 *              (which is wrong to do since ranges may overlap). This issue is
 *              fixed with **bpf_perf_event_read_value**\ (), which at the same
 *              time provides more features over the **bpf_perf_event_read**\
 *              () interface. Please refer to the description of
 *              **bpf_perf_event_read_value**\ () for details.
 *      Return
 *              The value of the perf event counter read from the map, or a
 *              negative error code in case of failure.
 *
 * int bpf_redirect(u32 ifindex, u64 flags)
 *      Description
 *              Redirect the packet to another net device of index *ifindex*.
 *              This helper is somewhat similar to **bpf_clone_redirect**\
 *              (), except that the packet is not cloned, which provides
 *              increased performance.
 *
 *              Except for XDP, both ingress and egress interfaces can be used
 *              for redirection. The **BPF_F_INGRESS** value in *flags* is used
 *              to make the distinction (ingress path is selected if the flag
 *              is present, egress path otherwise). Currently, XDP only
 *              supports redirection to the egress interface, and accepts no
 *              flag at all.
 *
 *              The same effect can be attained with the more generic
 *              **bpf_redirect_map**\ (), which requires specific maps to be
 *              used but offers better performance.
 *      Return
 *              For XDP, the helper returns **XDP_REDIRECT** on success or
 *              **XDP_ABORTED** on error. For other program types, the values
 *              are **TC_ACT_REDIRECT** on success or **TC_ACT_SHOT** on
 *              error.
 *
 * u32 bpf_get_route_realm(struct sk_buff *skb)
 *      Description
 *              Retrieve the realm or the route, that is to say the
 *              **tclassid** field of the destination for the *skb*. The
 *              indentifier retrieved is a user-provided tag, similar to the
 *              one used with the net_cls cgroup (see description for
 *              **bpf_get_cgroup_classid**\ () helper), but here this tag is
 *              held by a route (a destination entry), not by a task.
 *
 *              Retrieving this identifier works with the clsact TC egress hook
 *              (see also **tc-bpf(8)**), or alternatively on conventional
 *              classful egress qdiscs, but not on TC ingress path. In case of
 *              clsact TC egress hook, this has the advantage that, internally,
 *              the destination entry has not been dropped yet in the transmit
 *              path. Therefore, the destination entry does not need to be
 *              artificially held via **netif_keep_dst**\ () for a classful
 *              qdisc until the *skb* is freed.
 *
 *              This helper is available only if the kernel was compiled with
 *              **CONFIG_IP_ROUTE_CLASSID** configuration option.
 *      Return
 *              The realm of the route for the packet associated to *skb*, or 0
 *              if none was found.
 *
 * int bpf_perf_event_output(void *ctx, struct bpf_map *map, u64 flags, void *data, u64 size)
 *      Description
 *              Write raw *data* blob into a special BPF perf event held by
 *              *map* of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. This perf
 *              event must have the following attributes: **PERF_SAMPLE_RAW**
 *              as **sample_type**, **PERF_TYPE_SOFTWARE** as **type**, and
 *              **PERF_COUNT_SW_BPF_OUTPUT** as **config**.
 *
 *              The *flags* are used to indicate the index in *map* for which
 *              the value must be put, masked with **BPF_F_INDEX_MASK**.
 *              Alternatively, *flags* can be set to **BPF_F_CURRENT_CPU**
 *              to indicate that the index of the current CPU core should be
 *              used.
 *
 *              The value to write, of *size*, is passed through eBPF stack and
 *              pointed by *data*.
 *
 *              The context of the program *ctx* needs also be passed to the
 *              helper.
 *
 *              On user space, a program willing to read the values needs to
 *              call **perf_event_open**\ () on the perf event (either for
 *              one or for all CPUs) and to store the file descriptor into the
 *              *map*. This must be done before the eBPF program can send data
 *              into it. An example is available in file
 *              *samples/bpf/trace_output_user.c* in the Linux kernel source
 *              tree (the eBPF program counterpart is in
 *              *samples/bpf/trace_output_kern.c*).
 *
 *              **bpf_perf_event_output**\ () achieves better performance
 *              than **bpf_trace_printk**\ () for sharing data with user
 *              space, and is much better suitable for streaming data from eBPF
 *              programs.
 *
 *              Note that this helper is not restricted to tracing use cases
 *              and can be used with programs attached to TC or XDP as well,
 *              where it allows for passing data to user space listeners. Data
 *              can be:
 *
 *              * Only custom structs,
 *              * Only the packet payload, or
 *              * A combination of both.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_load_bytes(const void *skb, u32 offset, void *to, u32 len)
 *      Description
 *              This helper was provided as an easy way to load data from a
 *              packet. It can be used to load *len* bytes from *offset* from
 *              the packet associated to *skb*, into the buffer pointed by
 *              *to*.
 *
 *              Since Linux 4.7, usage of this helper has mostly been replaced
 *              by "direct packet access", enabling packet data to be
 *              manipulated with *skb*\ **->data** and *skb*\ **->data_end**
 *              pointing respectively to the first byte of packet data and to
 *              the byte after the last byte of packet data. However, it
 *              remains useful if one wishes to read large quantities of data
 *              at once from a packet into the eBPF stack.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_get_stackid(void *ctx, struct bpf_map *map, u64 flags)
 *      Description
 *              Walk a user or a kernel stack and return its id. To achieve
 *              this, the helper needs *ctx*, which is a pointer to the context
 *              on which the tracing program is executed, and a pointer to a
 *              *map* of type **BPF_MAP_TYPE_STACK_TRACE**.
 *
 *              The last argument, *flags*, holds the number of stack frames to
 *              skip (from 0 to 255), masked with
 *              **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
 *              a combination of the following flags:
 *
 *              **BPF_F_USER_STACK**
 *                      Collect a user space stack instead of a kernel stack.
 *              **BPF_F_FAST_STACK_CMP**
 *                      Compare stacks by hash only.
 *              **BPF_F_REUSE_STACKID**
 *                      If two different stacks hash into the same *stackid*,
 *                      discard the old one.
 *
 *              The stack id retrieved is a 32 bit long integer handle which
 *              can be further combined with other data (including other stack
 *              ids) and used as a key into maps. This can be useful for
 *              generating a variety of graphs (such as flame graphs or off-cpu
 *              graphs).
 *
 *              For walking a stack, this helper is an improvement over
 *              **bpf_probe_read**\ (), which can be used with unrolled loops
 *              but is not efficient and consumes a lot of eBPF instructions.
 *              Instead, **bpf_get_stackid**\ () can collect up to
 *              **PERF_MAX_STACK_DEPTH** both kernel and user frames. Note that
 *              this limit can be controlled with the **sysctl** program, and
 *              that it should be manually increased in order to profile long
 *              user stacks (such as stacks for Java programs). To do so, use:
 *
 *              ::
 *
 *                      # sysctl kernel.perf_event_max_stack=<new value>
 *      Return
 *              The positive or null stack id on success, or a negative error
 *              in case of failure.
 *
 * s64 bpf_csum_diff(__be32 *from, u32 from_size, __be32 *to, u32 to_size, __wsum seed)
 *      Description
 *              Compute a checksum difference, from the raw buffer pointed by
 *              *from*, of length *from_size* (that must be a multiple of 4),
 *              towards the raw buffer pointed by *to*, of size *to_size*
 *              (same remark). An optional *seed* can be added to the value
 *              (this can be cascaded, the seed may come from a previous call
 *              to the helper).
 *
 *              This is flexible enough to be used in several ways:
 *
 *              * With *from_size* == 0, *to_size* > 0 and *seed* set to
 *                checksum, it can be used when pushing new data.
 *              * With *from_size* > 0, *to_size* == 0 and *seed* set to
 *                checksum, it can be used when removing data from a packet.
 *              * With *from_size* > 0, *to_size* > 0 and *seed* set to 0, it
 *                can be used to compute a diff. Note that *from_size* and
 *                *to_size* do not need to be equal.
 *
 *              This helper can be used in combination with
 *              **bpf_l3_csum_replace**\ () and **bpf_l4_csum_replace**\ (), to
 *              which one can feed in the difference computed with
 *              **bpf_csum_diff**\ ().
 *      Return
 *              The checksum result, or a negative error code in case of
 *              failure.
 *
 * int bpf_skb_get_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)
 *      Description
 *              Retrieve tunnel options metadata for the packet associated to
 *              *skb*, and store the raw tunnel option data to the buffer *opt*
 *              of *size*.
 *
 *              This helper can be used with encapsulation devices that can
 *              operate in "collect metadata" mode (please refer to the related
 *              note in the description of **bpf_skb_get_tunnel_key**\ () for
 *              more details). A particular example where this can be used is
 *              in combination with the Geneve encapsulation protocol, where it
 *              allows for pushing (with **bpf_skb_get_tunnel_opt**\ () helper)
 *              and retrieving arbitrary TLVs (Type-Length-Value headers) from
 *              the eBPF program. This allows for full customization of these
 *              headers.
 *      Return
 *              The size of the option data retrieved.
 *
 * int bpf_skb_set_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)
 *      Description
 *              Set tunnel options metadata for the packet associated to *skb*
 *              to the option data contained in the raw buffer *opt* of *size*.
 *
 *              See also the description of the **bpf_skb_get_tunnel_opt**\ ()
 *              helper for additional information.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_change_proto(struct sk_buff *skb, __be16 proto, u64 flags)
 *      Description
 *              Change the protocol of the *skb* to *proto*. Currently
 *              supported are transition from IPv4 to IPv6, and from IPv6 to
 *              IPv4. The helper takes care of the groundwork for the
 *              transition, including resizing the socket buffer. The eBPF
 *              program is expected to fill the new headers, if any, via
 *              **skb_store_bytes**\ () and to recompute the checksums with
 *              **bpf_l3_csum_replace**\ () and **bpf_l4_csum_replace**\
 *              (). The main case for this helper is to perform NAT64
 *              operations out of an eBPF program.
 *
 *              Internally, the GSO type is marked as dodgy so that headers are
 *              checked and segments are recalculated by the GSO/GRO engine.
 *              The size for GSO target is adapted as well.
 *
 *              All values for *flags* are reserved for future usage, and must
 *              be left at zero.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_change_type(struct sk_buff *skb, u32 type)
 *      Description
 *              Change the packet type for the packet associated to *skb*. This
 *              comes down to setting *skb*\ **->pkt_type** to *type*, except
 *              the eBPF program does not have a write access to *skb*\
 *              **->pkt_type** beside this helper. Using a helper here allows
 *              for graceful handling of errors.
 *
 *              The major use case is to change incoming *skb*s to
 *              **PACKET_HOST** in a programmatic way instead of having to
 *              recirculate via **redirect**\ (..., **BPF_F_INGRESS**), for
 *              example.
 *
 *              Note that *type* only allows certain values. At this time, they
 *              are:
 *
 *              **PACKET_HOST**
 *                      Packet is for us.
 *              **PACKET_BROADCAST**
 *                      Send packet to all.
 *              **PACKET_MULTICAST**
 *                      Send packet to group.
 *              **PACKET_OTHERHOST**
 *                      Send packet to someone else.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_under_cgroup(struct sk_buff *skb, struct bpf_map *map, u32 index)
 *      Description
 *              Check whether *skb* is a descendant of the cgroup2 held by
 *              *map* of type **BPF_MAP_TYPE_CGROUP_ARRAY**, at *index*.
 *      Return
 *              The return value depends on the result of the test, and can be:
 *
 *              * 0, if the *skb* failed the cgroup2 descendant test.
 *              * 1, if the *skb* succeeded the cgroup2 descendant test.
 *              * A negative error code, if an error occurred.
 *
 * u32 bpf_get_hash_recalc(struct sk_buff *skb)
 *      Description
 *              Retrieve the hash of the packet, *skb*\ **->hash**. If it is
 *              not set, in particular if the hash was cleared due to mangling,
 *              recompute this hash. Later accesses to the hash can be done
 *              directly with *skb*\ **->hash**.
 *
 *              Calling **bpf_set_hash_invalid**\ (), changing a packet
 *              prototype with **bpf_skb_change_proto**\ (), or calling
 *              **bpf_skb_store_bytes**\ () with the
 *              **BPF_F_INVALIDATE_HASH** are actions susceptible to clear
 *              the hash and to trigger a new computation for the next call to
 *              **bpf_get_hash_recalc**\ ().
 *      Return
 *              The 32-bit hash.
 *
 * u64 bpf_get_current_task(void)
 *      Return
 *              A pointer to the current task struct.
 *
 * int bpf_probe_write_user(void *dst, const void *src, u32 len)
 *      Description
 *              Attempt in a safe way to write *len* bytes from the buffer
 *              *src* to *dst* in memory. It only works for threads that are in
 *              user context, and *dst* must be a valid user space address.
 *
 *              This helper should not be used to implement any kind of
 *              security mechanism because of TOC-TOU attacks, but rather to
 *              debug, divert, and manipulate execution of semi-cooperative
 *              processes.
 *
 *              Keep in mind that this feature is meant for experiments, and it
 *              has a risk of crashing the system and running programs.
 *              Therefore, when an eBPF program using this helper is attached,
 *              a warning including PID and process name is printed to kernel
 *              logs.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_current_task_under_cgroup(struct bpf_map *map, u32 index)
 *      Description
 *              Check whether the probe is being run is the context of a given
 *              subset of the cgroup2 hierarchy. The cgroup2 to test is held by
 *              *map* of type **BPF_MAP_TYPE_CGROUP_ARRAY**, at *index*.
 *      Return
 *              The return value depends on the result of the test, and can be:
 *
 *              * 0, if the *skb* task belongs to the cgroup2.
 *              * 1, if the *skb* task does not belong to the cgroup2.
 *              * A negative error code, if an error occurred.
 *
 * int bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)
 *      Description
 *              Resize (trim or grow) the packet associated to *skb* to the
 *              new *len*. The *flags* are reserved for future usage, and must
 *              be left at zero.
 *
 *              The basic idea is that the helper performs the needed work to
 *              change the size of the packet, then the eBPF program rewrites
 *              the rest via helpers like **bpf_skb_store_bytes**\ (),
 *              **bpf_l3_csum_replace**\ (), **bpf_l3_csum_replace**\ ()
 *              and others. This helper is a slow path utility intended for
 *              replies with control messages. And because it is targeted for
 *              slow path, the helper itself can afford to be slow: it
 *              implicitly linearizes, unclones and drops offloads from the
 *              *skb*.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_pull_data(struct sk_buff *skb, u32 len)
 *      Description
 *              Pull in non-linear data in case the *skb* is non-linear and not
 *              all of *len* are part of the linear section. Make *len* bytes
 *              from *skb* readable and writable. If a zero value is passed for
 *              *len*, then the whole length of the *skb* is pulled.
 *
 *              This helper is only needed for reading and writing with direct
 *              packet access.
 *
 *              For direct packet access, testing that offsets to access
 *              are within packet boundaries (test on *skb*\ **->data_end**) is
 *              susceptible to fail if offsets are invalid, or if the requested
 *              data is in non-linear parts of the *skb*. On failure the
 *              program can just bail out, or in the case of a non-linear
 *              buffer, use a helper to make the data available. The
 *              **bpf_skb_load_bytes**\ () helper is a first solution to access
 *              the data. Another one consists in using **bpf_skb_pull_data**
 *              to pull in once the non-linear parts, then retesting and
 *              eventually access the data.
 *
 *              At the same time, this also makes sure the *skb* is uncloned,
 *              which is a necessary condition for direct write. As this needs
 *              to be an invariant for the write part only, the verifier
 *              detects writes and adds a prologue that is calling
 *              **bpf_skb_pull_data()** to effectively unclone the *skb* from
 *              the very beginning in case it is indeed cloned.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * s64 bpf_csum_update(struct sk_buff *skb, __wsum csum)
 *      Description
 *              Add the checksum *csum* into *skb*\ **->csum** in case the
 *              driver has supplied a checksum for the entire packet into that
 *              field. Return an error otherwise. This helper is intended to be
 *              used in combination with **bpf_csum_diff**\ (), in particular
 *              when the checksum needs to be updated after data has been
 *              written into the packet through direct packet access.
 *      Return
 *              The checksum on success, or a negative error code in case of
 *              failure.
 *
 * void bpf_set_hash_invalid(struct sk_buff *skb)
 *      Description
 *              Invalidate the current *skb*\ **->hash**. It can be used after
 *              mangling on headers through direct packet access, in order to
 *              indicate that the hash is outdated and to trigger a
 *              recalculation the next time the kernel tries to access this
 *              hash or when the **bpf_get_hash_recalc**\ () helper is called.
 *
 * int bpf_get_numa_node_id(void)
 *      Description
 *              Return the id of the current NUMA node. The primary use case
 *              for this helper is the selection of sockets for the local NUMA
 *              node, when the program is attached to sockets using the
 *              **SO_ATTACH_REUSEPORT_EBPF** option (see also **socket(7)**),
 *              but the helper is also available to other eBPF program types,
 *              similarly to **bpf_get_smp_processor_id**\ ().
 *      Return
 *              The id of current NUMA node.
 *
 * int bpf_skb_change_head(struct sk_buff *skb, u32 len, u64 flags)
 *      Description
 *              Grows headroom of packet associated to *skb* and adjusts the
 *              offset of the MAC header accordingly, adding *len* bytes of
 *              space. It automatically extends and reallocates memory as
 *              required.
 *
 *              This helper can be used on a layer 3 *skb* to push a MAC header
 *              for redirection into a layer 2 device.
 *
 *              All values for *flags* are reserved for future usage, and must
 *              be left at zero.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_xdp_adjust_head(struct xdp_buff *xdp_md, int delta)
 *      Description
 *              Adjust (move) *xdp_md*\ **->data** by *delta* bytes. Note that
 *              it is possible to use a negative value for *delta*. This helper
 *              can be used to prepare the packet for pushing or popping
 *              headers.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read_str(void *dst, u32 size, const void *unsafe_ptr)
 *      Description
 *              Copy a NUL terminated string from an unsafe kernel address
 *              *unsafe_ptr* to *dst*. See bpf_probe_read_kernel_str() for
 *              more details.
 *
 *              Generally, use bpf_probe_read_user_str() or bpf_probe_read_kernel_str()
 *              instead.
 *      Return
 *              On success, the strictly positive length of the string,
 *              including the trailing NUL character. On error, a negative
 *              value.
 *
 * u64 bpf_get_socket_cookie(struct sk_buff *skb)
 *      Description
 *              If the **struct sk_buff** pointed by *skb* has a known socket,
 *              retrieve the cookie (generated by the kernel) of this socket.
 *              If no cookie has been set yet, generate a new cookie. Once
 *              generated, the socket cookie remains stable for the life of the
 *              socket. This helper can be useful for monitoring per socket
 *              networking traffic statistics as it provides a global socket
 *              identifier that can be assumed unique.
 *      Return
 *              A 8-byte long non-decreasing number on success, or 0 if the
 *              socket field is missing inside *skb*.
 *
 * u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)
 *      Description
 *              Equivalent to bpf_get_socket_cookie() helper that accepts
 *              *skb*, but gets socket from **struct bpf_sock_addr** context.
 *      Return
 *              A 8-byte long non-decreasing number.
 *
 * u64 bpf_get_socket_cookie(struct bpf_sock_ops *ctx)
 *      Description
 *              Equivalent to bpf_get_socket_cookie() helper that accepts
 *              *skb*, but gets socket from **struct bpf_sock_ops** context.
 *      Return
 *              A 8-byte long non-decreasing number.
 *
 * u32 bpf_get_socket_uid(struct sk_buff *skb)
 *      Return
 *              The owner UID of the socket associated to *skb*. If the socket
 *              is **NULL**, or if it is not a full socket (i.e. if it is a
 *              time-wait or a request socket instead), **overflowuid** value
 *              is returned (note that **overflowuid** might also be the actual
 *              UID value for the socket).
 *
 * u32 bpf_set_hash(struct sk_buff *skb, u32 hash)
 *      Description
 *              Set the full hash for *skb* (set the field *skb*\ **->hash**)
 *              to value *hash*.
 *      Return
 *              0
 *
 * int bpf_setsockopt(struct bpf_sock_ops *bpf_socket, int level, int optname, void *optval, int optlen)
 *      Description
 *              Emulate a call to **setsockopt()** on the socket associated to
 *              *bpf_socket*, which must be a full socket. The *level* at
 *              which the option resides and the name *optname* of the option
 *              must be specified, see **setsockopt(2)** for more information.
 *              The option value of length *optlen* is pointed by *optval*.
 *
 *              This helper actually implements a subset of **setsockopt()**.
 *              It supports the following *level*\ s:
 *
 *              * **SOL_SOCKET**, which supports the following *optname*\ s:
 *                **SO_RCVBUF**, **SO_SNDBUF**, **SO_MAX_PACING_RATE**,
 *                **SO_PRIORITY**, **SO_RCVLOWAT**, **SO_MARK**.
 *              * **IPPROTO_TCP**, which supports the following *optname*\ s:
 *                **TCP_CONGESTION**, **TCP_BPF_IW**,
 *                **TCP_BPF_SNDCWND_CLAMP**.
 *              * **IPPROTO_IP**, which supports *optname* **IP_TOS**.
 *              * **IPPROTO_IPV6**, which supports *optname* **IPV6_TCLASS**.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_adjust_room(struct sk_buff *skb, s32 len_diff, u32 mode, u64 flags)
 *      Description
 *              Grow or shrink the room for data in the packet associated to
 *              *skb* by *len_diff*, and according to the selected *mode*.
 *
 *              There are two supported modes at this time:
 *
 *              * **BPF_ADJ_ROOM_MAC**: Adjust room at the mac layer
 *                (room space is added or removed below the layer 2 header).
 *
 *              * **BPF_ADJ_ROOM_NET**: Adjust room at the network layer
 *                (room space is added or removed below the layer 3 header).
 *
 *              The following flags are supported at this time:
 *
 *              * **BPF_F_ADJ_ROOM_FIXED_GSO**: Do not adjust gso_size.
 *                Adjusting mss in this way is not allowed for datagrams.
 *
 *              * **BPF_F_ADJ_ROOM_ENCAP_L3_IPV4**,
 *                **BPF_F_ADJ_ROOM_ENCAP_L3_IPV6**:
 *                Any new space is reserved to hold a tunnel header.
 *                Configure skb offsets and other fields accordingly.
 *
 *              * **BPF_F_ADJ_ROOM_ENCAP_L4_GRE**,
 *                **BPF_F_ADJ_ROOM_ENCAP_L4_UDP**:
 *                Use with ENCAP_L3 flags to further specify the tunnel type.
 *
 *              * **BPF_F_ADJ_ROOM_ENCAP_L2**\ (*len*):
 *                Use with ENCAP_L3/L4 flags to further specify the tunnel
 *                type; *len* is the length of the inner MAC header.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)
 *      Description
 *              Redirect the packet to the endpoint referenced by *map* at
 *              index *key*. Depending on its type, this *map* can contain
 *              references to net devices (for forwarding packets through other
 *              ports), or to CPUs (for redirecting XDP frames to another CPU;
 *              but this is only implemented for native XDP (with driver
 *              support) as of this writing).
 *
 *              The lower two bits of *flags* are used as the return code if
 *              the map lookup fails. This is so that the return value can be
 *              one of the XDP program return codes up to XDP_TX, as chosen by
 *              the caller. Any higher bits in the *flags* argument must be
 *              unset.
 *
 *              When used to redirect packets to net devices, this helper
 *              provides a high performance increase over **bpf_redirect**\ ().
 *              This is due to various implementation details of the underlying
 *              mechanisms, one of which is the fact that **bpf_redirect_map**\
 *              () tries to send packet as a "bulk" to the device.
 *      Return
 *              **XDP_REDIRECT** on success, or **XDP_ABORTED** on error.
 *
 * int bpf_sk_redirect_map(struct sk_buff *skb, struct bpf_map *map, u32 key, u64 flags)
 *      Description
 *              Redirect the packet to the socket referenced by *map* (of type
 *              **BPF_MAP_TYPE_SOCKMAP**) at index *key*. Both ingress and
 *              egress interfaces can be used for redirection. The
 *              **BPF_F_INGRESS** value in *flags* is used to make the
 *              distinction (ingress path is selected if the flag is present,
 *              egress path otherwise). This is the only flag supported for now.
 *      Return
 *              **SK_PASS** on success, or **SK_DROP** on error.
 *
 * int bpf_sock_map_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags)
 *      Description
 *              Add an entry to, or update a *map* referencing sockets. The
 *              *skops* is used as a new value for the entry associated to
 *              *key*. *flags* is one of:
 *
 *              **BPF_NOEXIST**
 *                      The entry for *key* must not exist in the map.
 *              **BPF_EXIST**
 *                      The entry for *key* must already exist in the map.
 *              **BPF_ANY**
 *                      No condition on the existence of the entry for *key*.
 *
 *              If the *map* has eBPF programs (parser and verdict), those will
 *              be inherited by the socket being added. If the socket is
 *              already attached to eBPF programs, this results in an error.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_xdp_adjust_meta(struct xdp_buff *xdp_md, int delta)
 *      Description
 *              Adjust the address pointed by *xdp_md*\ **->data_meta** by
 *              *delta* (which can be positive or negative). Note that this
 *              operation modifies the address stored in *xdp_md*\ **->data**,
 *              so the latter must be loaded only after the helper has been
 *              called.
 *
 *              The use of *xdp_md*\ **->data_meta** is optional and programs
 *              are not required to use it. The rationale is that when the
 *              packet is processed with XDP (e.g. as DoS filter), it is
 *              possible to push further meta data along with it before passing
 *              to the stack, and to give the guarantee that an ingress eBPF
 *              program attached as a TC classifier on the same device can pick
 *              this up for further post-processing. Since TC works with socket
 *              buffers, it remains possible to set from XDP the **mark** or
 *              **priority** pointers, or other pointers for the socket buffer.
 *              Having this scratch space generic and programmable allows for
 *              more flexibility as the user is free to store whatever meta
 *              data they need.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_perf_event_read_value(struct bpf_map *map, u64 flags, struct bpf_perf_event_value *buf, u32 buf_size)
 *      Description
 *              Read the value of a perf event counter, and store it into *buf*
 *              of size *buf_size*. This helper relies on a *map* of type
 *              **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The nature of the perf event
 *              counter is selected when *map* is updated with perf event file
 *              descriptors. The *map* is an array whose size is the number of
 *              available CPUs, and each cell contains a value relative to one
 *              CPU. The value to retrieve is indicated by *flags*, that
 *              contains the index of the CPU to look up, masked with
 *              **BPF_F_INDEX_MASK**. Alternatively, *flags* can be set to
 *              **BPF_F_CURRENT_CPU** to indicate that the value for the
 *              current CPU should be retrieved.
 *
 *              This helper behaves in a way close to
 *              **bpf_perf_event_read**\ () helper, save that instead of
 *              just returning the value observed, it fills the *buf*
 *              structure. This allows for additional data to be retrieved: in
 *              particular, the enabled and running times (in *buf*\
 *              **->enabled** and *buf*\ **->running**, respectively) are
 *              copied. In general, **bpf_perf_event_read_value**\ () is
 *              recommended over **bpf_perf_event_read**\ (), which has some
 *              ABI issues and provides fewer functionalities.
 *
 *              These values are interesting, because hardware PMU (Performance
 *              Monitoring Unit) counters are limited resources. When there are
 *              more PMU based perf events opened than available counters,
 *              kernel will multiplex these events so each event gets certain
 *              percentage (but not all) of the PMU time. In case that
 *              multiplexing happens, the number of samples or counter value
 *              will not reflect the case compared to when no multiplexing
 *              occurs. This makes comparison between different runs difficult.
 *              Typically, the counter value should be normalized before
 *              comparing to other experiments. The usual normalization is done
 *              as follows.
 *
 *              ::
 *
 *                      normalized_counter = counter * t_enabled / t_running
 *
 *              Where t_enabled is the time enabled for event and t_running is
 *              the time running for event since last normalization. The
 *              enabled and running times are accumulated since the perf event
 *              open. To achieve scaling factor between two invocations of an
 *              eBPF program, users can can use CPU id as the key (which is
 *              typical for perf array usage model) to remember the previous
 *              value and do the calculation inside the eBPF program.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_perf_prog_read_value(struct bpf_perf_event_data *ctx, struct bpf_perf_event_value *buf, u32 buf_size)
 *      Description
 *              For en eBPF program attached to a perf event, retrieve the
 *              value of the event counter associated to *ctx* and store it in
 *              the structure pointed by *buf* and of size *buf_size*. Enabled
 *              and running times are also stored in the structure (see
 *              description of helper **bpf_perf_event_read_value**\ () for
 *              more details).
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_getsockopt(struct bpf_sock_ops *bpf_socket, int level, int optname, void *optval, int optlen)
 *      Description
 *              Emulate a call to **getsockopt()** on the socket associated to
 *              *bpf_socket*, which must be a full socket. The *level* at
 *              which the option resides and the name *optname* of the option
 *              must be specified, see **getsockopt(2)** for more information.
 *              The retrieved value is stored in the structure pointed by
 *              *opval* and of length *optlen*.
 *
 *              This helper actually implements a subset of **getsockopt()**.
 *              It supports the following *level*\ s:
 *
 *              * **IPPROTO_TCP**, which supports *optname*
 *                **TCP_CONGESTION**.
 *              * **IPPROTO_IP**, which supports *optname* **IP_TOS**.
 *              * **IPPROTO_IPV6**, which supports *optname* **IPV6_TCLASS**.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_override_return(struct pt_regs *regs, u64 rc)
 *      Description
 *              Used for error injection, this helper uses kprobes to override
 *              the return value of the probed function, and to set it to *rc*.
 *              The first argument is the context *regs* on which the kprobe
 *              works.
 *
 *              This helper works by setting setting the PC (program counter)
 *              to an override function which is run in place of the original
 *              probed function. This means the probed function is not run at
 *              all. The replacement function just returns with the required
 *              value.
 *
 *              This helper has security implications, and thus is subject to
 *              restrictions. It is only available if the kernel was compiled
 *              with the **CONFIG_BPF_KPROBE_OVERRIDE** configuration
 *              option, and in this case it only works on functions tagged with
 *              **ALLOW_ERROR_INJECTION** in the kernel code.
 *
 *              Also, the helper is only available for the architectures having
 *              the CONFIG_FUNCTION_ERROR_INJECTION option. As of this writing,
 *              x86 architecture is the only one to support this feature.
 *      Return
 *              0
 *
 * int bpf_sock_ops_cb_flags_set(struct bpf_sock_ops *bpf_sock, int argval)
 *      Description
 *              Attempt to set the value of the **bpf_sock_ops_cb_flags** field
 *              for the full TCP socket associated to *bpf_sock_ops* to
 *              *argval*.
 *
 *              The primary use of this field is to determine if there should
 *              be calls to eBPF programs of type
 *              **BPF_PROG_TYPE_SOCK_OPS** at various points in the TCP
 *              code. A program of the same type can change its value, per
 *              connection and as necessary, when the connection is
 *              established. This field is directly accessible for reading, but
 *              this helper must be used for updates in order to return an
 *              error if an eBPF program tries to set a callback that is not
 *              supported in the current kernel.
 *
 *              *argval* is a flag array which can combine these flags:
 *
 *              * **BPF_SOCK_OPS_RTO_CB_FLAG** (retransmission time out)
 *              * **BPF_SOCK_OPS_RETRANS_CB_FLAG** (retransmission)
 *              * **BPF_SOCK_OPS_STATE_CB_FLAG** (TCP state change)
 *              * **BPF_SOCK_OPS_RTT_CB_FLAG** (every RTT)
 *
 *              Therefore, this function can be used to clear a callback flag by
 *              setting the appropriate bit to zero. e.g. to disable the RTO
 *              callback:
 *
 *              **bpf_sock_ops_cb_flags_set(bpf_sock,**
 *                      **bpf_sock->bpf_sock_ops_cb_flags & ~BPF_SOCK_OPS_RTO_CB_FLAG)**
 *
 *              Here are some examples of where one could call such eBPF
 *              program:
 *
 *              * When RTO fires.
 *              * When a packet is retransmitted.
 *              * When the connection terminates.
 *              * When a packet is sent.
 *              * When a packet is received.
 *      Return
 *              Code **-EINVAL** if the socket is not a full TCP socket;
 *              otherwise, a positive number containing the bits that could not
 *              be set is returned (which comes down to 0 if all bits were set
 *              as required).
 *
 * int bpf_msg_redirect_map(struct sk_msg_buff *msg, struct bpf_map *map, u32 key, u64 flags)
 *      Description
 *              This helper is used in programs implementing policies at the
 *              socket level. If the message *msg* is allowed to pass (i.e. if
 *              the verdict eBPF program returns **SK_PASS**), redirect it to
 *              the socket referenced by *map* (of type
 *              **BPF_MAP_TYPE_SOCKMAP**) at index *key*. Both ingress and
 *              egress interfaces can be used for redirection. The
 *              **BPF_F_INGRESS** value in *flags* is used to make the
 *              distinction (ingress path is selected if the flag is present,
 *              egress path otherwise). This is the only flag supported for now.
 *      Return
 *              **SK_PASS** on success, or **SK_DROP** on error.
 *
 * int bpf_msg_apply_bytes(struct sk_msg_buff *msg, u32 bytes)
 *      Description
 *              For socket policies, apply the verdict of the eBPF program to
 *              the next *bytes* (number of bytes) of message *msg*.
 *
 *              For example, this helper can be used in the following cases:
 *
 *              * A single **sendmsg**\ () or **sendfile**\ () system call
 *                contains multiple logical messages that the eBPF program is
 *                supposed to read and for which it should apply a verdict.
 *              * An eBPF program only cares to read the first *bytes* of a
 *                *msg*. If the message has a large payload, then setting up
 *                and calling the eBPF program repeatedly for all bytes, even
 *                though the verdict is already known, would create unnecessary
 *                overhead.
 *
 *              When called from within an eBPF program, the helper sets a
 *              counter internal to the BPF infrastructure, that is used to
 *              apply the last verdict to the next *bytes*. If *bytes* is
 *              smaller than the current data being processed from a
 *              **sendmsg**\ () or **sendfile**\ () system call, the first
 *              *bytes* will be sent and the eBPF program will be re-run with
 *              the pointer for start of data pointing to byte number *bytes*
 *              **+ 1**. If *bytes* is larger than the current data being
 *              processed, then the eBPF verdict will be applied to multiple
 *              **sendmsg**\ () or **sendfile**\ () calls until *bytes* are
 *              consumed.
 *
 *              Note that if a socket closes with the internal counter holding
 *              a non-zero value, this is not a problem because data is not
 *              being buffered for *bytes* and is sent as it is received.
 *      Return
 *              0
 *
 * int bpf_msg_cork_bytes(struct sk_msg_buff *msg, u32 bytes)
 *      Description
 *              For socket policies, prevent the execution of the verdict eBPF
 *              program for message *msg* until *bytes* (byte number) have been
 *              accumulated.
 *
 *              This can be used when one needs a specific number of bytes
 *              before a verdict can be assigned, even if the data spans
 *              multiple **sendmsg**\ () or **sendfile**\ () calls. The extreme
 *              case would be a user calling **sendmsg**\ () repeatedly with
 *              1-byte long message segments. Obviously, this is bad for
 *              performance, but it is still valid. If the eBPF program needs
 *              *bytes* bytes to validate a header, this helper can be used to
 *              prevent the eBPF program to be called again until *bytes* have
 *              been accumulated.
 *      Return
 *              0
 *
 * int bpf_msg_pull_data(struct sk_msg_buff *msg, u32 start, u32 end, u64 flags)
 *      Description
 *              For socket policies, pull in non-linear data from user space
 *              for *msg* and set pointers *msg*\ **->data** and *msg*\
 *              **->data_end** to *start* and *end* bytes offsets into *msg*,
 *              respectively.
 *
 *              If a program of type **BPF_PROG_TYPE_SK_MSG** is run on a
 *              *msg* it can only parse data that the (**data**, **data_end**)
 *              pointers have already consumed. For **sendmsg**\ () hooks this
 *              is likely the first scatterlist element. But for calls relying
 *              on the **sendpage** handler (e.g. **sendfile**\ ()) this will
 *              be the range (**0**, **0**) because the data is shared with
 *              user space and by default the objective is to avoid allowing
 *              user space to modify data while (or after) eBPF verdict is
 *              being decided. This helper can be used to pull in data and to
 *              set the start and end pointer to given values. Data will be
 *              copied if necessary (i.e. if data was not linear and if start
 *              and end pointers do not point to the same chunk).
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *
 *              All values for *flags* are reserved for future usage, and must
 *              be left at zero.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_bind(struct bpf_sock_addr *ctx, struct sockaddr *addr, int addr_len)
 *      Description
 *              Bind the socket associated to *ctx* to the address pointed by
 *              *addr*, of length *addr_len*. This allows for making outgoing
 *              connection from the desired IP address, which can be useful for
 *              example when all processes inside a cgroup should use one
 *              single IP address on a host that has multiple IP configured.
 *
 *              This helper works for IPv4 and IPv6, TCP and UDP sockets. The
 *              domain (*addr*\ **->sa_family**) must be **AF_INET** (or
 *              **AF_INET6**). Looking for a free port to bind to can be
 *              expensive, therefore binding to port is not permitted by the
 *              helper: *addr*\ **->sin_port** (or **sin6_port**, respectively)
 *              must be set to zero.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_xdp_adjust_tail(struct xdp_buff *xdp_md, int delta)
 *      Description
 *              Adjust (move) *xdp_md*\ **->data_end** by *delta* bytes. It is
 *              only possible to shrink the packet as of this writing,
 *              therefore *delta* must be a negative integer.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_get_xfrm_state(struct sk_buff *skb, u32 index, struct bpf_xfrm_state *xfrm_state, u32 size, u64 flags)
 *      Description
 *              Retrieve the XFRM state (IP transform framework, see also
 *              **ip-xfrm(8)**) at *index* in XFRM "security path" for *skb*.
 *
 *              The retrieved value is stored in the **struct bpf_xfrm_state**
 *              pointed by *xfrm_state* and of length *size*.
 *
 *              All values for *flags* are reserved for future usage, and must
 *              be left at zero.
 *
 *              This helper is available only if the kernel was compiled with
 *              **CONFIG_XFRM** configuration option.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_get_stack(void *ctx, void *buf, u32 size, u64 flags)
 *      Description
 *              Return a user or a kernel stack in bpf program provided buffer.
 *              To achieve this, the helper needs *ctx*, which is a pointer
 *              to the context on which the tracing program is executed.
 *              To store the stacktrace, the bpf program provides *buf* with
 *              a nonnegative *size*.
 *
 *              The last argument, *flags*, holds the number of stack frames to
 *              skip (from 0 to 255), masked with
 *              **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
 *              the following flags:
 *
 *              **BPF_F_USER_STACK**
 *                      Collect a user space stack instead of a kernel stack.
 *              **BPF_F_USER_BUILD_ID**
 *                      Collect buildid+offset instead of ips for user stack,
 *                      only valid if **BPF_F_USER_STACK** is also specified.
 *
 *              **bpf_get_stack**\ () can collect up to
 *              **PERF_MAX_STACK_DEPTH** both kernel and user frames, subject
 *              to sufficient large buffer size. Note that
 *              this limit can be controlled with the **sysctl** program, and
 *              that it should be manually increased in order to profile long
 *              user stacks (such as stacks for Java programs). To do so, use:
 *
 *              ::
 *
 *                      # sysctl kernel.perf_event_max_stack=<new value>
 *      Return
 *              A non-negative value equal to or less than *size* on success,
 *              or a negative error in case of failure.
 *
 * int bpf_skb_load_bytes_relative(const void *skb, u32 offset, void *to, u32 len, u32 start_header)
 *      Description
 *              This helper is similar to **bpf_skb_load_bytes**\ () in that
 *              it provides an easy way to load *len* bytes from *offset*
 *              from the packet associated to *skb*, into the buffer pointed
 *              by *to*. The difference to **bpf_skb_load_bytes**\ () is that
 *              a fifth argument *start_header* exists in order to select a
 *              base offset to start from. *start_header* can be one of:
 *
 *              **BPF_HDR_START_MAC**
 *                      Base offset to load data from is *skb*'s mac header.
 *              **BPF_HDR_START_NET**
 *                      Base offset to load data from is *skb*'s network header.
 *
 *              In general, "direct packet access" is the preferred method to
 *              access packet data, however, this helper is in particular useful
 *              in socket filters where *skb*\ **->data** does not always point
 *              to the start of the mac header and where "direct packet access"
 *              is not available.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_fib_lookup(void *ctx, struct bpf_fib_lookup *params, int plen, u32 flags)
 *      Description
 *              Do FIB lookup in kernel tables using parameters in *params*.
 *              If lookup is successful and result shows packet is to be
 *              forwarded, the neighbor tables are searched for the nexthop.
 *              If successful (ie., FIB lookup shows forwarding and nexthop
 *              is resolved), the nexthop address is returned in ipv4_dst
 *              or ipv6_dst based on family, smac is set to mac address of
 *              egress device, dmac is set to nexthop mac address, rt_metric
 *              is set to metric from route (IPv4/IPv6 only), and ifindex
 *              is set to the device index of the nexthop from the FIB lookup.
 *
 *              *plen* argument is the size of the passed in struct.
 *              *flags* argument can be a combination of one or more of the
 *              following values:
 *
 *              **BPF_FIB_LOOKUP_DIRECT**
 *                      Do a direct table lookup vs full lookup using FIB
 *                      rules.
 *              **BPF_FIB_LOOKUP_OUTPUT**
 *                      Perform lookup from an egress perspective (default is
 *                      ingress).
 *
 *              *ctx* is either **struct xdp_md** for XDP programs or
 *              **struct sk_buff** tc cls_act programs.
 *      Return
 *              * < 0 if any input argument is invalid
 *              *   0 on success (packet is forwarded, nexthop neighbor exists)
 *              * > 0 one of **BPF_FIB_LKUP_RET_** codes explaining why the
 *                packet is not forwarded or needs assist from full stack
 *
 * int bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags)
 *      Description
 *              Add an entry to, or update a sockhash *map* referencing sockets.
 *              The *skops* is used as a new value for the entry associated to
 *              *key*. *flags* is one of:
 *
 *              **BPF_NOEXIST**
 *                      The entry for *key* must not exist in the map.
 *              **BPF_EXIST**
 *                      The entry for *key* must already exist in the map.
 *              **BPF_ANY**
 *                      No condition on the existence of the entry for *key*.
 *
 *              If the *map* has eBPF programs (parser and verdict), those will
 *              be inherited by the socket being added. If the socket is
 *              already attached to eBPF programs, this results in an error.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_msg_redirect_hash(struct sk_msg_buff *msg, struct bpf_map *map, void *key, u64 flags)
 *      Description
 *              This helper is used in programs implementing policies at the
 *              socket level. If the message *msg* is allowed to pass (i.e. if
 *              the verdict eBPF program returns **SK_PASS**), redirect it to
 *              the socket referenced by *map* (of type
 *              **BPF_MAP_TYPE_SOCKHASH**) using hash *key*. Both ingress and
 *              egress interfaces can be used for redirection. The
 *              **BPF_F_INGRESS** value in *flags* is used to make the
 *              distinction (ingress path is selected if the flag is present,
 *              egress path otherwise). This is the only flag supported for now.
 *      Return
 *              **SK_PASS** on success, or **SK_DROP** on error.
 *
 * int bpf_sk_redirect_hash(struct sk_buff *skb, struct bpf_map *map, void *key, u64 flags)
 *      Description
 *              This helper is used in programs implementing policies at the
 *              skb socket level. If the sk_buff *skb* is allowed to pass (i.e.
 *              if the verdeict eBPF program returns **SK_PASS**), redirect it
 *              to the socket referenced by *map* (of type
 *              **BPF_MAP_TYPE_SOCKHASH**) using hash *key*. Both ingress and
 *              egress interfaces can be used for redirection. The
 *              **BPF_F_INGRESS** value in *flags* is used to make the
 *              distinction (ingress path is selected if the flag is present,
 *              egress otherwise). This is the only flag supported for now.
 *      Return
 *              **SK_PASS** on success, or **SK_DROP** on error.
 *
 * int bpf_lwt_push_encap(struct sk_buff *skb, u32 type, void *hdr, u32 len)
 *      Description
 *              Encapsulate the packet associated to *skb* within a Layer 3
 *              protocol header. This header is provided in the buffer at
 *              address *hdr*, with *len* its size in bytes. *type* indicates
 *              the protocol of the header and can be one of:
 *
 *              **BPF_LWT_ENCAP_SEG6**
 *                      IPv6 encapsulation with Segment Routing Header
 *                      (**struct ipv6_sr_hdr**). *hdr* only contains the SRH,
 *                      the IPv6 header is computed by the kernel.
 *              **BPF_LWT_ENCAP_SEG6_INLINE**
 *                      Only works if *skb* contains an IPv6 packet. Insert a
 *                      Segment Routing Header (**struct ipv6_sr_hdr**) inside
 *                      the IPv6 header.
 *              **BPF_LWT_ENCAP_IP**
 *                      IP encapsulation (GRE/GUE/IPIP/etc). The outer header
 *                      must be IPv4 or IPv6, followed by zero or more
 *                      additional headers, up to **LWT_BPF_MAX_HEADROOM**
 *                      total bytes in all prepended headers. Please note that
 *                      if **skb_is_gso**\ (*skb*) is true, no more than two
 *                      headers can be prepended, and the inner header, if
 *                      present, should be either GRE or UDP/GUE.
 *
 *              **BPF_LWT_ENCAP_SEG6**\ \* types can be called by BPF programs
 *              of type **BPF_PROG_TYPE_LWT_IN**; **BPF_LWT_ENCAP_IP** type can
 *              be called by bpf programs of types **BPF_PROG_TYPE_LWT_IN** and
 *              **BPF_PROG_TYPE_LWT_XMIT**.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_lwt_seg6_store_bytes(struct sk_buff *skb, u32 offset, const void *from, u32 len)
 *      Description
 *              Store *len* bytes from address *from* into the packet
 *              associated to *skb*, at *offset*. Only the flags, tag and TLVs
 *              inside the outermost IPv6 Segment Routing Header can be
 *              modified through this helper.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_lwt_seg6_adjust_srh(struct sk_buff *skb, u32 offset, s32 delta)
 *      Description
 *              Adjust the size allocated to TLVs in the outermost IPv6
 *              Segment Routing Header contained in the packet associated to
 *              *skb*, at position *offset* by *delta* bytes. Only offsets
 *              after the segments are accepted. *delta* can be as well
 *              positive (growing) as negative (shrinking).
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_lwt_seg6_action(struct sk_buff *skb, u32 action, void *param, u32 param_len)
 *      Description
 *              Apply an IPv6 Segment Routing action of type *action* to the
 *              packet associated to *skb*. Each action takes a parameter
 *              contained at address *param*, and of length *param_len* bytes.
 *              *action* can be one of:
 *
 *              **SEG6_LOCAL_ACTION_END_X**
 *                      End.X action: Endpoint with Layer-3 cross-connect.
 *                      Type of *param*: **struct in6_addr**.
 *              **SEG6_LOCAL_ACTION_END_T**
 *                      End.T action: Endpoint with specific IPv6 table lookup.
 *                      Type of *param*: **int**.
 *              **SEG6_LOCAL_ACTION_END_B6**
 *                      End.B6 action: Endpoint bound to an SRv6 policy.
 *                      Type of *param*: **struct ipv6_sr_hdr**.
 *              **SEG6_LOCAL_ACTION_END_B6_ENCAP**
 *                      End.B6.Encap action: Endpoint bound to an SRv6
 *                      encapsulation policy.
 *                      Type of *param*: **struct ipv6_sr_hdr**.
 *
 *              A call to this helper is susceptible to change the underlying
 *              packet buffer. Therefore, at load time, all checks on pointers
 *              previously done by the verifier are invalidated and must be
 *              performed again, if the helper is used in combination with
 *              direct packet access.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_rc_repeat(void *ctx)
 *      Description
 *              This helper is used in programs implementing IR decoding, to
 *              report a successfully decoded repeat key message. This delays
 *              the generation of a key up event for previously generated
 *              key down event.
 *
 *              Some IR protocols like NEC have a special IR message for
 *              repeating last button, for when a button is held down.
 *
 *              The *ctx* should point to the lirc sample as passed into
 *              the program.
 *
 *              This helper is only available is the kernel was compiled with
 *              the **CONFIG_BPF_LIRC_MODE2** configuration option set to
 *              "**y**".
 *      Return
 *              0
 *
 * int bpf_rc_keydown(void *ctx, u32 protocol, u64 scancode, u32 toggle)
 *      Description
 *              This helper is used in programs implementing IR decoding, to
 *              report a successfully decoded key press with *scancode*,
 *              *toggle* value in the given *protocol*. The scancode will be
 *              translated to a keycode using the rc keymap, and reported as
 *              an input key down event. After a period a key up event is
 *              generated. This period can be extended by calling either
 *              **bpf_rc_keydown**\ () again with the same values, or calling
 *              **bpf_rc_repeat**\ ().
 *
 *              Some protocols include a toggle bit, in case the button was
 *              released and pressed again between consecutive scancodes.
 *
 *              The *ctx* should point to the lirc sample as passed into
 *              the program.
 *
 *              The *protocol* is the decoded protocol number (see
 *              **enum rc_proto** for some predefined values).
 *
 *              This helper is only available is the kernel was compiled with
 *              the **CONFIG_BPF_LIRC_MODE2** configuration option set to
 *              "**y**".
 *      Return
 *              0
 *
 * u64 bpf_skb_cgroup_id(struct sk_buff *skb)
 *      Description
 *              Return the cgroup v2 id of the socket associated with the *skb*.
 *              This is roughly similar to the **bpf_get_cgroup_classid**\ ()
 *              helper for cgroup v1 by providing a tag resp. identifier that
 *              can be matched on or used for map lookups e.g. to implement
 *              policy. The cgroup v2 id of a given path in the hierarchy is
 *              exposed in user space through the f_handle API in order to get
 *              to the same 64-bit id.
 *
 *              This helper can be used on TC egress path, but not on ingress,
 *              and is available only if the kernel was compiled with the
 *              **CONFIG_SOCK_CGROUP_DATA** configuration option.
 *      Return
 *              The id is returned or 0 in case the id could not be retrieved.
 *
 * u64 bpf_get_current_cgroup_id(void)
 *      Return
 *              A 64-bit integer containing the current cgroup id based
 *              on the cgroup within which the current task is running.
 *
 * void *bpf_get_local_storage(void *map, u64 flags)
 *      Description
 *              Get the pointer to the local storage area.
 *              The type and the size of the local storage is defined
 *              by the *map* argument.
 *              The *flags* meaning is specific for each map type,
 *              and has to be 0 for cgroup local storage.
 *
 *              Depending on the BPF program type, a local storage area
 *              can be shared between multiple instances of the BPF program,
 *              running simultaneously.
 *
 *              A user should care about the synchronization by himself.
 *              For example, by using the **BPF_STX_XADD** instruction to alter
 *              the shared data.
 *      Return
 *              A pointer to the local storage area.
 *
 * int bpf_sk_select_reuseport(struct sk_reuseport_md *reuse, struct bpf_map *map, void *key, u64 flags)
 *      Description
 *              Select a **SO_REUSEPORT** socket from a
 *              **BPF_MAP_TYPE_REUSEPORT_ARRAY** *map*.
 *              It checks the selected socket is matching the incoming
 *              request in the socket buffer.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * u64 bpf_skb_ancestor_cgroup_id(struct sk_buff *skb, int ancestor_level)
 *      Description
 *              Return id of cgroup v2 that is ancestor of cgroup associated
 *              with the *skb* at the *ancestor_level*.  The root cgroup is at
 *              *ancestor_level* zero and each step down the hierarchy
 *              increments the level. If *ancestor_level* == level of cgroup
 *              associated with *skb*, then return value will be same as that
 *              of **bpf_skb_cgroup_id**\ ().
 *
 *              The helper is useful to implement policies based on cgroups
 *              that are upper in hierarchy than immediate cgroup associated
 *              with *skb*.
 *
 *              The format of returned id and helper limitations are same as in
 *              **bpf_skb_cgroup_id**\ ().
 *      Return
 *              The id is returned or 0 in case the id could not be retrieved.
 *
 * struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)
 *      Description
 *              Look for TCP socket matching *tuple*, optionally in a child
 *              network namespace *netns*. The return value must be checked,
 *              and if non-**NULL**, released via **bpf_sk_release**\ ().
 *
 *              The *ctx* should point to the context of the program, such as
 *              the skb or socket (depending on the hook in use). This is used
 *              to determine the base network namespace for the lookup.
 *
 *              *tuple_size* must be one of:
 *
 *              **sizeof**\ (*tuple*\ **->ipv4**)
 *                      Look for an IPv4 socket.
 *              **sizeof**\ (*tuple*\ **->ipv6**)
 *                      Look for an IPv6 socket.
 *
 *              If the *netns* is a negative signed 32-bit integer, then the
 *              socket lookup table in the netns associated with the *ctx* will
 *              will be used. For the TC hooks, this is the netns of the device
 *              in the skb. For socket hooks, this is the netns of the socket.
 *              If *netns* is any other signed 32-bit value greater than or
 *              equal to zero then it specifies the ID of the netns relative to
 *              the netns associated with the *ctx*. *netns* values beyond the
 *              range of 32-bit integers are reserved for future use.
 *
 *              All values for *flags* are reserved for future usage, and must
 *              be left at zero.
 *
 *              This helper is available only if the kernel was compiled with
 *              **CONFIG_NET** configuration option.
 *      Return
 *              Pointer to **struct bpf_sock**, or **NULL** in case of failure.
 *              For sockets with reuseport option, the **struct bpf_sock**
 *              result is from *reuse*\ **->socks**\ [] using the hash of the
 *              tuple.
 *
 * struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)
 *      Description
 *              Look for UDP socket matching *tuple*, optionally in a child
 *              network namespace *netns*. The return value must be checked,
 *              and if non-**NULL**, released via **bpf_sk_release**\ ().
 *
 *              The *ctx* should point to the context of the program, such as
 *              the skb or socket (depending on the hook in use). This is used
 *              to determine the base network namespace for the lookup.
 *
 *              *tuple_size* must be one of:
 *
 *              **sizeof**\ (*tuple*\ **->ipv4**)
 *                      Look for an IPv4 socket.
 *              **sizeof**\ (*tuple*\ **->ipv6**)
 *                      Look for an IPv6 socket.
 *
 *              If the *netns* is a negative signed 32-bit integer, then the
 *              socket lookup table in the netns associated with the *ctx* will
 *              will be used. For the TC hooks, this is the netns of the device
 *              in the skb. For socket hooks, this is the netns of the socket.
 *              If *netns* is any other signed 32-bit value greater than or
 *              equal to zero then it specifies the ID of the netns relative to
 *              the netns associated with the *ctx*. *netns* values beyond the
 *              range of 32-bit integers are reserved for future use.
 *
 *              All values for *flags* are reserved for future usage, and must
 *              be left at zero.
 *
 *              This helper is available only if the kernel was compiled with
 *              **CONFIG_NET** configuration option.
 *      Return
 *              Pointer to **struct bpf_sock**, or **NULL** in case of failure.
 *              For sockets with reuseport option, the **struct bpf_sock**
 *              result is from *reuse*\ **->socks**\ [] using the hash of the
 *              tuple.
 *
 * int bpf_sk_release(struct bpf_sock *sock)
 *      Description
 *              Release the reference held by *sock*. *sock* must be a
 *              non-**NULL** pointer that was returned from
 *              **bpf_sk_lookup_xxx**\ ().
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_map_push_elem(struct bpf_map *map, const void *value, u64 flags)
 *      Description
 *              Push an element *value* in *map*. *flags* is one of:
 *
 *              **BPF_EXIST**
 *                      If the queue/stack is full, the oldest element is
 *                      removed to make room for this.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_map_pop_elem(struct bpf_map *map, void *value)
 *      Description
 *              Pop an element from *map*.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_map_peek_elem(struct bpf_map *map, void *value)
 *      Description
 *              Get an element from *map* without removing it.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_msg_push_data(struct sk_msg_buff *msg, u32 start, u32 len, u64 flags)
 *      Description
 *              For socket policies, insert *len* bytes into *msg* at offset
 *              *start*.
 *
 *              If a program of type **BPF_PROG_TYPE_SK_MSG** is run on a
 *              *msg* it may want to insert metadata or options into the *msg*.
 *              This can later be read and used by any of the lower layer BPF
 *              hooks.
 *
 *              This helper may fail if under memory pressure (a malloc
 *              fails) in these cases BPF programs will get an appropriate
 *              error and BPF programs will need to handle them.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_msg_pop_data(struct sk_msg_buff *msg, u32 start, u32 len, u64 flags)
 *      Description
 *              Will remove *len* bytes from a *msg* starting at byte *start*.
 *              This may result in **ENOMEM** errors under certain situations if
 *              an allocation and copy are required due to a full ring buffer.
 *              However, the helper will try to avoid doing the allocation
 *              if possible. Other errors can occur if input parameters are
 *              invalid either due to *start* byte not being valid part of *msg*
 *              payload and/or *pop* value being to large.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_rc_pointer_rel(void *ctx, s32 rel_x, s32 rel_y)
 *      Description
 *              This helper is used in programs implementing IR decoding, to
 *              report a successfully decoded pointer movement.
 *
 *              The *ctx* should point to the lirc sample as passed into
 *              the program.
 *
 *              This helper is only available is the kernel was compiled with
 *              the **CONFIG_BPF_LIRC_MODE2** configuration option set to
 *              "**y**".
 *      Return
 *              0
 *
 * int bpf_spin_lock(struct bpf_spin_lock *lock)
 *      Description
 *              Acquire a spinlock represented by the pointer *lock*, which is
 *              stored as part of a value of a map. Taking the lock allows to
 *              safely update the rest of the fields in that value. The
 *              spinlock can (and must) later be released with a call to
 *              **bpf_spin_unlock**\ (\ *lock*\ ).
 *
 *              Spinlocks in BPF programs come with a number of restrictions
 *              and constraints:
 *
 *              * **bpf_spin_lock** objects are only allowed inside maps of
 *                types **BPF_MAP_TYPE_HASH** and **BPF_MAP_TYPE_ARRAY** (this
 *                list could be extended in the future).
 *              * BTF description of the map is mandatory.
 *              * The BPF program can take ONE lock at a time, since taking two
 *                or more could cause dead locks.
 *              * Only one **struct bpf_spin_lock** is allowed per map element.
 *              * When the lock is taken, calls (either BPF to BPF or helpers)
 *                are not allowed.
 *              * The **BPF_LD_ABS** and **BPF_LD_IND** instructions are not
 *                allowed inside a spinlock-ed region.
 *              * The BPF program MUST call **bpf_spin_unlock**\ () to release
 *                the lock, on all execution paths, before it returns.
 *              * The BPF program can access **struct bpf_spin_lock** only via
 *                the **bpf_spin_lock**\ () and **bpf_spin_unlock**\ ()
 *                helpers. Loading or storing data into the **struct
 *                bpf_spin_lock** *lock*\ **;** field of a map is not allowed.
 *              * To use the **bpf_spin_lock**\ () helper, the BTF description
 *                of the map value must be a struct and have **struct
 *                bpf_spin_lock** *anyname*\ **;** field at the top level.
 *                Nested lock inside another struct is not allowed.
 *              * The **struct bpf_spin_lock** *lock* field in a map value must
 *                be aligned on a multiple of 4 bytes in that value.
 *              * Syscall with command **BPF_MAP_LOOKUP_ELEM** does not copy
 *                the **bpf_spin_lock** field to user space.
 *              * Syscall with command **BPF_MAP_UPDATE_ELEM**, or update from
 *                a BPF program, do not update the **bpf_spin_lock** field.
 *              * **bpf_spin_lock** cannot be on the stack or inside a
 *                networking packet (it can only be inside of a map values).
 *              * **bpf_spin_lock** is available to root only.
 *              * Tracing programs and socket filter programs cannot use
 *                **bpf_spin_lock**\ () due to insufficient preemption checks
 *                (but this may change in the future).
 *              * **bpf_spin_lock** is not allowed in inner maps of map-in-map.
 *      Return
 *              0
 *
 * int bpf_spin_unlock(struct bpf_spin_lock *lock)
 *      Description
 *              Release the *lock* previously locked by a call to
 *              **bpf_spin_lock**\ (\ *lock*\ ).
 *      Return
 *              0
 *
 * struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)
 *      Description
 *              This helper gets a **struct bpf_sock** pointer such
 *              that all the fields in this **bpf_sock** can be accessed.
 *      Return
 *              A **struct bpf_sock** pointer on success, or **NULL** in
 *              case of failure.
 *
 * struct bpf_tcp_sock *bpf_tcp_sock(struct bpf_sock *sk)
 *      Description
 *              This helper gets a **struct bpf_tcp_sock** pointer from a
 *              **struct bpf_sock** pointer.
 *      Return
 *              A **struct bpf_tcp_sock** pointer on success, or **NULL** in
 *              case of failure.
 *
 * int bpf_skb_ecn_set_ce(struct sk_buff *skb)
 *      Description
 *              Set ECN (Explicit Congestion Notification) field of IP header
 *              to **CE** (Congestion Encountered) if current value is **ECT**
 *              (ECN Capable Transport). Otherwise, do nothing. Works with IPv6
 *              and IPv4.
 *      Return
 *              1 if the **CE** flag is set (either by the current helper call
 *              or because it was already present), 0 if it is not set.
 *
 * struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *sk)
 *      Description
 *              Return a **struct bpf_sock** pointer in **TCP_LISTEN** state.
 *              **bpf_sk_release**\ () is unnecessary and not allowed.
 *      Return
 *              A **struct bpf_sock** pointer on success, or **NULL** in
 *              case of failure.
 *
 * struct bpf_sock *bpf_skc_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple, u32 tuple_size, u64 netns, u64 flags)
 *      Description
 *              Look for TCP socket matching *tuple*, optionally in a child
 *              network namespace *netns*. The return value must be checked,
 *              and if non-**NULL**, released via **bpf_sk_release**\ ().
 *
 *              This function is identical to **bpf_sk_lookup_tcp**\ (), except
 *              that it also returns timewait or request sockets. Use
 *              **bpf_sk_fullsock**\ () or **bpf_tcp_sock**\ () to access the
 *              full structure.
 *
 *              This helper is available only if the kernel was compiled with
 *              **CONFIG_NET** configuration option.
 *      Return
 *              Pointer to **struct bpf_sock**, or **NULL** in case of failure.
 *              For sockets with reuseport option, the **struct bpf_sock**
 *              result is from *reuse*\ **->socks**\ [] using the hash of the
 *              tuple.
 *
 * int bpf_tcp_check_syncookie(struct bpf_sock *sk, void *iph, u32 iph_len, struct tcphdr *th, u32 th_len)
 *      Description
 *              Check whether *iph* and *th* contain a valid SYN cookie ACK for
 *              the listening socket in *sk*.
 *
 *              *iph* points to the start of the IPv4 or IPv6 header, while
 *              *iph_len* contains **sizeof**\ (**struct iphdr**) or
 *              **sizeof**\ (**struct ip6hdr**).
 *
 *              *th* points to the start of the TCP header, while *th_len*
 *              contains **sizeof**\ (**struct tcphdr**).
 *
 *      Return
 *              0 if *iph* and *th* are a valid SYN cookie ACK, or a negative
 *              error otherwise.
 *
 * int bpf_sysctl_get_name(struct bpf_sysctl *ctx, char *buf, size_t buf_len, u64 flags)
 *      Description
 *              Get name of sysctl in /proc/sys/ and copy it into provided by
 *              program buffer *buf* of size *buf_len*.
 *
 *              The buffer is always NUL terminated, unless it's zero-sized.
 *
 *              If *flags* is zero, full name (e.g. "net/ipv4/tcp_mem") is
 *              copied. Use **BPF_F_SYSCTL_BASE_NAME** flag to copy base name
 *              only (e.g. "tcp_mem").
 *      Return
 *              Number of character copied (not including the trailing NUL).
 *
 *              **-E2BIG** if the buffer wasn't big enough (*buf* will contain
 *              truncated name in this case).
 *
 * int bpf_sysctl_get_current_value(struct bpf_sysctl *ctx, char *buf, size_t buf_len)
 *      Description
 *              Get current value of sysctl as it is presented in /proc/sys
 *              (incl. newline, etc), and copy it as a string into provided
 *              by program buffer *buf* of size *buf_len*.
 *
 *              The whole value is copied, no matter what file position user
 *              space issued e.g. sys_read at.
 *
 *              The buffer is always NUL terminated, unless it's zero-sized.
 *      Return
 *              Number of character copied (not including the trailing NUL).
 *
 *              **-E2BIG** if the buffer wasn't big enough (*buf* will contain
 *              truncated name in this case).
 *
 *              **-EINVAL** if current value was unavailable, e.g. because
 *              sysctl is uninitialized and read returns -EIO for it.
 *
 * int bpf_sysctl_get_new_value(struct bpf_sysctl *ctx, char *buf, size_t buf_len)
 *      Description
 *              Get new value being written by user space to sysctl (before
 *              the actual write happens) and copy it as a string into
 *              provided by program buffer *buf* of size *buf_len*.
 *
 *              User space may write new value at file position > 0.
 *
 *              The buffer is always NUL terminated, unless it's zero-sized.
 *      Return
 *              Number of character copied (not including the trailing NUL).
 *
 *              **-E2BIG** if the buffer wasn't big enough (*buf* will contain
 *              truncated name in this case).
 *
 *              **-EINVAL** if sysctl is being read.
 *
 * int bpf_sysctl_set_new_value(struct bpf_sysctl *ctx, const char *buf, size_t buf_len)
 *      Description
 *              Override new value being written by user space to sysctl with
 *              value provided by program in buffer *buf* of size *buf_len*.
 *
 *              *buf* should contain a string in same form as provided by user
 *              space on sysctl write.
 *
 *              User space may write new value at file position > 0. To override
 *              the whole sysctl value file position should be set to zero.
 *      Return
 *              0 on success.
 *
 *              **-E2BIG** if the *buf_len* is too big.
 *
 *              **-EINVAL** if sysctl is being read.
 *
 * int bpf_strtol(const char *buf, size_t buf_len, u64 flags, long *res)
 *      Description
 *              Convert the initial part of the string from buffer *buf* of
 *              size *buf_len* to a long integer according to the given base
 *              and save the result in *res*.
 *
 *              The string may begin with an arbitrary amount of white space
 *              (as determined by **isspace**\ (3)) followed by a single
 *              optional '**-**' sign.
 *
 *              Five least significant bits of *flags* encode base, other bits
 *              are currently unused.
 *
 *              Base must be either 8, 10, 16 or 0 to detect it automatically
 *              similar to user space **strtol**\ (3).
 *      Return
 *              Number of characters consumed on success. Must be positive but
 *              no more than *buf_len*.
 *
 *              **-EINVAL** if no valid digits were found or unsupported base
 *              was provided.
 *
 *              **-ERANGE** if resulting value was out of range.
 *
 * int bpf_strtoul(const char *buf, size_t buf_len, u64 flags, unsigned long *res)
 *      Description
 *              Convert the initial part of the string from buffer *buf* of
 *              size *buf_len* to an unsigned long integer according to the
 *              given base and save the result in *res*.
 *
 *              The string may begin with an arbitrary amount of white space
 *              (as determined by **isspace**\ (3)).
 *
 *              Five least significant bits of *flags* encode base, other bits
 *              are currently unused.
 *
 *              Base must be either 8, 10, 16 or 0 to detect it automatically
 *              similar to user space **strtoul**\ (3).
 *      Return
 *              Number of characters consumed on success. Must be positive but
 *              no more than *buf_len*.
 *
 *              **-EINVAL** if no valid digits were found or unsupported base
 *              was provided.
 *
 *              **-ERANGE** if resulting value was out of range.
 *
 * void *bpf_sk_storage_get(struct bpf_map *map, struct bpf_sock *sk, void *value, u64 flags)
 *      Description
 *              Get a bpf-local-storage from a *sk*.
 *
 *              Logically, it could be thought of getting the value from
 *              a *map* with *sk* as the **key**.  From this
 *              perspective,  the usage is not much different from
 *              **bpf_map_lookup_elem**\ (*map*, **&**\ *sk*) except this
 *              helper enforces the key must be a full socket and the map must
 *              be a **BPF_MAP_TYPE_SK_STORAGE** also.
 *
 *              Underneath, the value is stored locally at *sk* instead of
 *              the *map*.  The *map* is used as the bpf-local-storage
 *              "type". The bpf-local-storage "type" (i.e. the *map*) is
 *              searched against all bpf-local-storages residing at *sk*.
 *
 *              An optional *flags* (**BPF_SK_STORAGE_GET_F_CREATE**) can be
 *              used such that a new bpf-local-storage will be
 *              created if one does not exist.  *value* can be used
 *              together with **BPF_SK_STORAGE_GET_F_CREATE** to specify
 *              the initial value of a bpf-local-storage.  If *value* is
 *              **NULL**, the new bpf-local-storage will be zero initialized.
 *      Return
 *              A bpf-local-storage pointer is returned on success.
 *
 *              **NULL** if not found or there was an error in adding
 *              a new bpf-local-storage.
 *
 * int bpf_sk_storage_delete(struct bpf_map *map, struct bpf_sock *sk)
 *      Description
 *              Delete a bpf-local-storage from a *sk*.
 *      Return
 *              0 on success.
 *
 *              **-ENOENT** if the bpf-local-storage cannot be found.
 *
 * int bpf_send_signal(u32 sig)
 *      Description
 *              Send signal *sig* to the current task.
 *      Return
 *              0 on success or successfully queued.
 *
 *              **-EBUSY** if work queue under nmi is full.
 *
 *              **-EINVAL** if *sig* is invalid.
 *
 *              **-EPERM** if no permission to send the *sig*.
 *
 *              **-EAGAIN** if bpf program can try again.
 *
 * s64 bpf_tcp_gen_syncookie(struct bpf_sock *sk, void *iph, u32 iph_len, struct tcphdr *th, u32 th_len)
 *      Description
 *              Try to issue a SYN cookie for the packet with corresponding
 *              IP/TCP headers, *iph* and *th*, on the listening socket in *sk*.
 *
 *              *iph* points to the start of the IPv4 or IPv6 header, while
 *              *iph_len* contains **sizeof**\ (**struct iphdr**) or
 *              **sizeof**\ (**struct ip6hdr**).
 *
 *              *th* points to the start of the TCP header, while *th_len*
 *              contains the length of the TCP header.
 *
 *      Return
 *              On success, lower 32 bits hold the generated SYN cookie in
 *              followed by 16 bits which hold the MSS value for that cookie,
 *              and the top 16 bits are unused.
 *
 *              On failure, the returned value is one of the following:
 *
 *              **-EINVAL** SYN cookie cannot be issued due to error
 *
 *              **-ENOENT** SYN cookie should not be issued (no SYN flood)
 *
 *              **-EOPNOTSUPP** kernel configuration does not enable SYN cookies
 *
 *              **-EPROTONOSUPPORT** IP packet version is not 4 or 6
 *
 * int bpf_skb_output(void *ctx, struct bpf_map *map, u64 flags, void *data, u64 size)
 *      Description
 *              Write raw *data* blob into a special BPF perf event held by
 *              *map* of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. This perf
 *              event must have the following attributes: **PERF_SAMPLE_RAW**
 *              as **sample_type**, **PERF_TYPE_SOFTWARE** as **type**, and
 *              **PERF_COUNT_SW_BPF_OUTPUT** as **config**.
 *
 *              The *flags* are used to indicate the index in *map* for which
 *              the value must be put, masked with **BPF_F_INDEX_MASK**.
 *              Alternatively, *flags* can be set to **BPF_F_CURRENT_CPU**
 *              to indicate that the index of the current CPU core should be
 *              used.
 *
 *              The value to write, of *size*, is passed through eBPF stack and
 *              pointed by *data*.
 *
 *              *ctx* is a pointer to in-kernel struct sk_buff.
 *
 *              This helper is similar to **bpf_perf_event_output**\ () but
 *              restricted to raw_tracepoint bpf programs.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read_user(void *dst, u32 size, const void *unsafe_ptr)
 *      Description
 *              Safely attempt to read *size* bytes from user space address
 *              *unsafe_ptr* and store the data in *dst*.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
 *      Description
 *              Safely attempt to read *size* bytes from kernel space address
 *              *unsafe_ptr* and store the data in *dst*.
 *      Return
 *              0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read_user_str(void *dst, u32 size, const void *unsafe_ptr)
 *      Description
 *              Copy a NUL terminated string from an unsafe user address
 *              *unsafe_ptr* to *dst*. The *size* should include the
 *              terminating NUL byte. In case the string length is smaller than
 *              *size*, the target is not padded with further NUL bytes. If the
 *              string length is larger than *size*, just *size*-1 bytes are
 *              copied and the last byte is set to NUL.
 *
 *              On success, the length of the copied string is returned. This
 *              makes this helper useful in tracing programs for reading
 *              strings, and more importantly to get its length at runtime. See
 *              the following snippet:
 *
 *              ::
 *
 *                      SEC("kprobe/sys_open")
 *                      void bpf_sys_open(struct pt_regs *ctx)
 *                      {
 *                              char buf[PATHLEN]; // PATHLEN is defined to 256
 *                              int res = bpf_probe_read_user_str(buf, sizeof(buf),
 *                                                                ctx->di);
 *
 *                              // Consume buf, for example push it to
 *                              // userspace via bpf_perf_event_output(); we
 *                              // can use res (the string length) as event
 *                              // size, after checking its boundaries.
 *                      }
 *
 *              In comparison, using **bpf_probe_read_user()** helper here
 *              instead to read the string would require to estimate the length
 *              at compile time, and would often result in copying more memory
 *              than necessary.
 *
 *              Another useful use case is when parsing individual process
 *              arguments or individual environment variables navigating
 *              *current*\ **->mm->arg_start** and *current*\
 *              **->mm->env_start**: using this helper and the return value,
 *              one can quickly iterate at the right offset of the memory area.
 *      Return
 *              On success, the strictly positive length of the string,
 *              including the trailing NUL character. On error, a negative
 *              value.
 *
 * int bpf_probe_read_kernel_str(void *dst, u32 size, const void *unsafe_ptr)
 *      Description
 *              Copy a NUL terminated string from an unsafe kernel address *unsafe_ptr*
 *              to *dst*. Same semantics as with bpf_probe_read_user_str() apply.
 *      Return
 *              On success, the strictly positive length of the string, including
 *              the trailing NUL character. On error, a negative value.
 */
#define __BPF_FUNC_MAPPER(FN)           \
        FN(unspec),                     \
        FN(map_lookup_elem),            \
        FN(map_update_elem),            \
        FN(map_delete_elem),            \
        FN(probe_read),                 \
        FN(ktime_get_ns),               \
        FN(trace_printk),               \
        FN(get_prandom_u32),            \
        FN(get_smp_processor_id),       \
        FN(skb_store_bytes),            \
        FN(l3_csum_replace),            \
        FN(l4_csum_replace),            \
        FN(tail_call),                  \
        FN(clone_redirect),             \
        FN(get_current_pid_tgid),       \
        FN(get_current_uid_gid),        \
        FN(get_current_comm),           \
        FN(get_cgroup_classid),         \
        FN(skb_vlan_push),              \
        FN(skb_vlan_pop),               \
        FN(skb_get_tunnel_key),         \
        FN(skb_set_tunnel_key),         \
        FN(perf_event_read),            \
        FN(redirect),                   \
        FN(get_route_realm),            \
        FN(perf_event_output),          \
        FN(skb_load_bytes),             \
        FN(get_stackid),                \
        FN(csum_diff),                  \
        FN(skb_get_tunnel_opt),         \
        FN(skb_set_tunnel_opt),         \
        FN(skb_change_proto),           \
        FN(skb_change_type),            \
        FN(skb_under_cgroup),           \
        FN(get_hash_recalc),            \
        FN(get_current_task),           \
        FN(probe_write_user),           \
        FN(current_task_under_cgroup),  \
        FN(skb_change_tail),            \
        FN(skb_pull_data),              \
        FN(csum_update),                \
        FN(set_hash_invalid),           \
        FN(get_numa_node_id),           \
        FN(skb_change_head),            \
        FN(xdp_adjust_head),            \
        FN(probe_read_str),             \
        FN(get_socket_cookie),          \
        FN(get_socket_uid),             \
        FN(set_hash),                   \
        FN(setsockopt),                 \
        FN(skb_adjust_room),            \
        FN(redirect_map),               \
        FN(sk_redirect_map),            \
        FN(sock_map_update),            \
        FN(xdp_adjust_meta),            \
        FN(perf_event_read_value),      \
        FN(perf_prog_read_value),       \
        FN(getsockopt),                 \
        FN(override_return),            \
        FN(sock_ops_cb_flags_set),      \
        FN(msg_redirect_map),           \
        FN(msg_apply_bytes),            \
        FN(msg_cork_bytes),             \
        FN(msg_pull_data),              \
        FN(bind),                       \
        FN(xdp_adjust_tail),            \
        FN(skb_get_xfrm_state),         \
        FN(get_stack),                  \
        FN(skb_load_bytes_relative),    \
        FN(fib_lookup),                 \
        FN(sock_hash_update),           \
        FN(msg_redirect_hash),          \
        FN(sk_redirect_hash),           \
        FN(lwt_push_encap),             \
        FN(lwt_seg6_store_bytes),       \
        FN(lwt_seg6_adjust_srh),        \
        FN(lwt_seg6_action),            \
        FN(rc_repeat),                  \
        FN(rc_keydown),                 \
        FN(skb_cgroup_id),              \
        FN(get_current_cgroup_id),      \
        FN(get_local_storage),          \
        FN(sk_select_reuseport),        \
        FN(skb_ancestor_cgroup_id),     \
        FN(sk_lookup_tcp),              \
        FN(sk_lookup_udp),              \
        FN(sk_release),                 \
        FN(map_push_elem),              \
        FN(map_pop_elem),               \
        FN(map_peek_elem),              \
        FN(msg_push_data),              \
        FN(msg_pop_data),               \
        FN(rc_pointer_rel),             \
        FN(spin_lock),                  \
        FN(spin_unlock),                \
        FN(sk_fullsock),                \
        FN(tcp_sock),                   \
        FN(skb_ecn_set_ce),             \
        FN(get_listener_sock),          \
        FN(skc_lookup_tcp),             \
        FN(tcp_check_syncookie),        \
        FN(sysctl_get_name),            \
        FN(sysctl_get_current_value),   \
        FN(sysctl_get_new_value),       \
        FN(sysctl_set_new_value),       \
        FN(strtol),                     \
        FN(strtoul),                    \
        FN(sk_storage_get),             \
        FN(sk_storage_delete),          \
        FN(send_signal),                \
        FN(tcp_gen_syncookie),          \
        FN(skb_output),                 \
        FN(probe_read_user),            \
        FN(probe_read_kernel),          \
        FN(probe_read_user_str),        \
        FN(probe_read_kernel_str),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
 * function eBPF program intends to call
 */
#define __BPF_ENUM_FN(x) BPF_FUNC_ ## x
enum bpf_func_id {
        __BPF_FUNC_MAPPER(__BPF_ENUM_FN)
        __BPF_FUNC_MAX_ID,
};
#undef __BPF_ENUM_FN

/* All flags used by eBPF helper functions, placed here. */

/* BPF_FUNC_skb_store_bytes flags. */
#define BPF_F_RECOMPUTE_CSUM            (1ULL << 0)
#define BPF_F_INVALIDATE_HASH           (1ULL << 1)

/* BPF_FUNC_l3_csum_replace and BPF_FUNC_l4_csum_replace flags.
 * First 4 bits are for passing the header field size.
 */
#define BPF_F_HDR_FIELD_MASK            0xfULL

/* BPF_FUNC_l4_csum_replace flags. */
#define BPF_F_PSEUDO_HDR                (1ULL << 4)
#define BPF_F_MARK_MANGLED_0            (1ULL << 5)
#define BPF_F_MARK_ENFORCE              (1ULL << 6)

/* BPF_FUNC_clone_redirect and BPF_FUNC_redirect flags. */
#define BPF_F_INGRESS                   (1ULL << 0)

/* BPF_FUNC_skb_set_tunnel_key and BPF_FUNC_skb_get_tunnel_key flags. */
#define BPF_F_TUNINFO_IPV6              (1ULL << 0)

/* flags for both BPF_FUNC_get_stackid and BPF_FUNC_get_stack. */
#define BPF_F_SKIP_FIELD_MASK           0xffULL
#define BPF_F_USER_STACK                (1ULL << 8)
/* flags used by BPF_FUNC_get_stackid only. */
#define BPF_F_FAST_STACK_CMP            (1ULL << 9)
#define BPF_F_REUSE_STACKID             (1ULL << 10)
/* flags used by BPF_FUNC_get_stack only. */
#define BPF_F_USER_BUILD_ID             (1ULL << 11)

/* BPF_FUNC_skb_set_tunnel_key flags. */
#define BPF_F_ZERO_CSUM_TX              (1ULL << 1)
#define BPF_F_DONT_FRAGMENT             (1ULL << 2)
#define BPF_F_SEQ_NUMBER                (1ULL << 3)

/* BPF_FUNC_perf_event_output, BPF_FUNC_perf_event_read and
 * BPF_FUNC_perf_event_read_value flags.
 */
#define BPF_F_INDEX_MASK                0xffffffffULL
#define BPF_F_CURRENT_CPU               BPF_F_INDEX_MASK
/* BPF_FUNC_perf_event_output for sk_buff input context. */
#define BPF_F_CTXLEN_MASK               (0xfffffULL << 32)

/* Current network namespace */
#define BPF_F_CURRENT_NETNS             (-1L)

/* BPF_FUNC_skb_adjust_room flags. */
#define BPF_F_ADJ_ROOM_FIXED_GSO        (1ULL << 0)

#define BPF_ADJ_ROOM_ENCAP_L2_MASK      0xff
#define BPF_ADJ_ROOM_ENCAP_L2_SHIFT     56

#define BPF_F_ADJ_ROOM_ENCAP_L3_IPV4    (1ULL << 1)
#define BPF_F_ADJ_ROOM_ENCAP_L3_IPV6    (1ULL << 2)
#define BPF_F_ADJ_ROOM_ENCAP_L4_GRE     (1ULL << 3)
#define BPF_F_ADJ_ROOM_ENCAP_L4_UDP     (1ULL << 4)
#define BPF_F_ADJ_ROOM_ENCAP_L2(len)    (((__u64)len & \
                                          BPF_ADJ_ROOM_ENCAP_L2_MASK) \
                                         << BPF_ADJ_ROOM_ENCAP_L2_SHIFT)

/* BPF_FUNC_sysctl_get_name flags. */
#define BPF_F_SYSCTL_BASE_NAME          (1ULL << 0)

/* BPF_FUNC_sk_storage_get flags */
#define BPF_SK_STORAGE_GET_F_CREATE     (1ULL << 0)

/* Mode for BPF_FUNC_skb_adjust_room helper. */
enum bpf_adj_room_mode {
        BPF_ADJ_ROOM_NET,
        BPF_ADJ_ROOM_MAC,
};

/* Mode for BPF_FUNC_skb_load_bytes_relative helper. */
enum bpf_hdr_start_off {
        BPF_HDR_START_MAC,
        BPF_HDR_START_NET,
};

/* Encapsulation type for BPF_FUNC_lwt_push_encap helper. */
enum bpf_lwt_encap_mode {
        BPF_LWT_ENCAP_SEG6,
        BPF_LWT_ENCAP_SEG6_INLINE,
        BPF_LWT_ENCAP_IP,
};

#define __bpf_md_ptr(type, name)        \
union {                                 \
        type name;                      \
        __u64 :64;                      \
} __attribute__((aligned(8)))

/* user accessible mirror of in-kernel sk_buff.
 * new fields can only be added to the end of this structure
 */
struct __sk_buff {
        __u32 len;
        __u32 pkt_type;
        __u32 mark;
        __u32 queue_mapping;
        __u32 protocol;
        __u32 vlan_present;
        __u32 vlan_tci;
        __u32 vlan_proto;
        __u32 priority;
        __u32 ingress_ifindex;
        __u32 ifindex;
        __u32 tc_index;
        __u32 cb[5];
        __u32 hash;
        __u32 tc_classid;
        __u32 data;
        __u32 data_end;
        __u32 napi_id;

        /* Accessed by BPF_PROG_TYPE_sk_skb types from here to ... */
        __u32 family;
        __u32 remote_ip4;       /* Stored in network byte order */
        __u32 local_ip4;        /* Stored in network byte order */
        __u32 remote_ip6[4];    /* Stored in network byte order */
        __u32 local_ip6[4];     /* Stored in network byte order */
        __u32 remote_port;      /* Stored in network byte order */
        __u32 local_port;       /* stored in host byte order */
        /* ... here. */

        __u32 data_meta;
        __bpf_md_ptr(struct bpf_flow_keys *, flow_keys);
        __u64 tstamp;
        __u32 wire_len;
        __u32 gso_segs;
        __bpf_md_ptr(struct bpf_sock *, sk);
};

struct bpf_tunnel_key {
        __u32 tunnel_id;
        union {
                __u32 remote_ipv4;
                __u32 remote_ipv6[4];
        };
        __u8 tunnel_tos;
        __u8 tunnel_ttl;
        __u16 tunnel_ext;       /* Padding, future use. */
        __u32 tunnel_label;
};

/* user accessible mirror of in-kernel xfrm_state.
 * new fields can only be added to the end of this structure
 */
struct bpf_xfrm_state {
        __u32 reqid;
        __u32 spi;      /* Stored in network byte order */
        __u16 family;
        __u16 ext;      /* Padding, future use. */
        union {
                __u32 remote_ipv4;      /* Stored in network byte order */
                __u32 remote_ipv6[4];   /* Stored in network byte order */
        };
};

/* Generic BPF return codes which all BPF program types may support.
 * The values are binary compatible with their TC_ACT_* counter-part to
 * provide backwards compatibility with existing SCHED_CLS and SCHED_ACT
 * programs.
 *
 * XDP is handled seprately, see XDP_*.
 */
enum bpf_ret_code {
        BPF_OK = 0,
        /* 1 reserved */
        BPF_DROP = 2,
        /* 3-6 reserved */
        BPF_REDIRECT = 7,
        /* >127 are reserved for prog type specific return codes.
         *
         * BPF_LWT_REROUTE: used by BPF_PROG_TYPE_LWT_IN and
         *    BPF_PROG_TYPE_LWT_XMIT to indicate that skb had been
         *    changed and should be routed based on its new L3 header.
         *    (This is an L3 redirect, as opposed to L2 redirect
         *    represented by BPF_REDIRECT above).
         */
        BPF_LWT_REROUTE = 128,
};

struct bpf_sock {
        __u32 bound_dev_if;
        __u32 family;
        __u32 type;
        __u32 protocol;
        __u32 mark;
        __u32 priority;
        /* IP address also allows 1 and 2 bytes access */
        __u32 src_ip4;
        __u32 src_ip6[4];
        __u32 src_port;         /* host byte order */
        __u32 dst_port;         /* network byte order */
        __u32 dst_ip4;
        __u32 dst_ip6[4];
        __u32 state;
};

struct bpf_tcp_sock {
        __u32 snd_cwnd;         /* Sending congestion window            */
        __u32 srtt_us;          /* smoothed round trip time << 3 in usecs */
        __u32 rtt_min;
        __u32 snd_ssthresh;     /* Slow start size threshold            */
        __u32 rcv_nxt;          /* What we want to receive next         */
        __u32 snd_nxt;          /* Next sequence we send                */
        __u32 snd_una;          /* First byte we want an ack for        */
        __u32 mss_cache;        /* Cached effective mss, not including SACKS */
        __u32 ecn_flags;        /* ECN status bits.                     */
        __u32 rate_delivered;   /* saved rate sample: packets delivered */
        __u32 rate_interval_us; /* saved rate sample: time elapsed */
        __u32 packets_out;      /* Packets which are "in flight"        */
        __u32 retrans_out;      /* Retransmitted packets out            */
        __u32 total_retrans;    /* Total retransmits for entire connection */
        __u32 segs_in;          /* RFC4898 tcpEStatsPerfSegsIn
                                 * total number of segments in.
                                 */
        __u32 data_segs_in;     /* RFC4898 tcpEStatsPerfDataSegsIn
                                 * total number of data segments in.
                                 */
        __u32 segs_out;         /* RFC4898 tcpEStatsPerfSegsOut
                                 * The total number of segments sent.
                                 */
        __u32 data_segs_out;    /* RFC4898 tcpEStatsPerfDataSegsOut
                                 * total number of data segments sent.
                                 */
        __u32 lost_out;         /* Lost packets                 */
        __u32 sacked_out;       /* SACK'd packets                       */
        __u64 bytes_received;   /* RFC4898 tcpEStatsAppHCThruOctetsReceived
                                 * sum(delta(rcv_nxt)), or how many bytes
                                 * were acked.
                                 */
        __u64 bytes_acked;      /* RFC4898 tcpEStatsAppHCThruOctetsAcked
                                 * sum(delta(snd_una)), or how many bytes
                                 * were acked.
                                 */
        __u32 dsack_dups;       /* RFC4898 tcpEStatsStackDSACKDups
                                 * total number of DSACK blocks received
                                 */
        __u32 delivered;        /* Total data packets delivered incl. rexmits */
        __u32 delivered_ce;     /* Like the above but only ECE marked packets */
        __u32 icsk_retransmits; /* Number of unrecovered [RTO] timeouts */
};

struct bpf_sock_tuple {
        union {
                struct {
                        __be32 saddr;
                        __be32 daddr;
                        __be16 sport;
                        __be16 dport;
                } ipv4;
                struct {
                        __be32 saddr[4];
                        __be32 daddr[4];
                        __be16 sport;
                        __be16 dport;
                } ipv6;
        };
};

struct bpf_xdp_sock {
        __u32 queue_id;
};

#define XDP_PACKET_HEADROOM 256

/* User return codes for XDP prog type.
 * A valid XDP program must return one of these defined values. All other
 * return codes are reserved for future use. Unknown return codes will
 * result in packet drops and a warning via bpf_warn_invalid_xdp_action().
 */
enum xdp_action {
        XDP_ABORTED = 0,
        XDP_DROP,
        XDP_PASS,
        XDP_TX,
        XDP_REDIRECT,
};

/* user accessible metadata for XDP packet hook
 * new fields must be added to the end of this structure
 */
struct xdp_md {
        __u32 data;
        __u32 data_end;
        __u32 data_meta;
        /* Below access go through struct xdp_rxq_info */
        __u32 ingress_ifindex; /* rxq->dev->ifindex */
        __u32 rx_queue_index;  /* rxq->queue_index  */
};

enum sk_action {
        SK_DROP = 0,
        SK_PASS,
};

/* user accessible metadata for SK_MSG packet hook, new fields must
 * be added to the end of this structure
 */
struct sk_msg_md {
        __bpf_md_ptr(void *, data);
        __bpf_md_ptr(void *, data_end);

        __u32 family;
        __u32 remote_ip4;       /* Stored in network byte order */
        __u32 local_ip4;        /* Stored in network byte order */
        __u32 remote_ip6[4];    /* Stored in network byte order */
        __u32 local_ip6[4];     /* Stored in network byte order */
        __u32 remote_port;      /* Stored in network byte order */
        __u32 local_port;       /* stored in host byte order */
        __u32 size;             /* Total size of sk_msg */
};

struct sk_reuseport_md {
        /*
         * Start of directly accessible data. It begins from
         * the tcp/udp header.
         */
        __bpf_md_ptr(void *, data);
        /* End of directly accessible data */
        __bpf_md_ptr(void *, data_end);
        /*
         * Total length of packet (starting from the tcp/udp header).
         * Note that the directly accessible bytes (data_end - data)
         * could be less than this "len".  Those bytes could be
         * indirectly read by a helper "bpf_skb_load_bytes()".
         */
        __u32 len;
        /*
         * Eth protocol in the mac header (network byte order). e.g.
         * ETH_P_IP(0x0800) and ETH_P_IPV6(0x86DD)
         */
        __u32 eth_protocol;
        __u32 ip_protocol;      /* IP protocol. e.g. IPPROTO_TCP, IPPROTO_UDP */
        __u32 bind_inany;       /* Is sock bound to an INANY address? */
        __u32 hash;             /* A hash of the packet 4 tuples */
};

#define BPF_TAG_SIZE    8

struct bpf_prog_info {
        __u32 type;
        __u32 id;
        __u8  tag[BPF_TAG_SIZE];
        __u32 jited_prog_len;
        __u32 xlated_prog_len;
        __aligned_u64 jited_prog_insns;
        __aligned_u64 xlated_prog_insns;
        __u64 load_time;        /* ns since boottime */
        __u32 created_by_uid;
        __u32 nr_map_ids;
        __aligned_u64 map_ids;
        char name[BPF_OBJ_NAME_LEN];
        __u32 ifindex;
        __u32 gpl_compatible:1;
        __u32 :31; /* alignment pad */
        __u64 netns_dev;
        __u64 netns_ino;
        __u32 nr_jited_ksyms;
        __u32 nr_jited_func_lens;
        __aligned_u64 jited_ksyms;
        __aligned_u64 jited_func_lens;
        __u32 btf_id;
        __u32 func_info_rec_size;
        __aligned_u64 func_info;
        __u32 nr_func_info;
        __u32 nr_line_info;
        __aligned_u64 line_info;
        __aligned_u64 jited_line_info;
        __u32 nr_jited_line_info;
        __u32 line_info_rec_size;
        __u32 jited_line_info_rec_size;
        __u32 nr_prog_tags;
        __aligned_u64 prog_tags;
        __u64 run_time_ns;
        __u64 run_cnt;
} __attribute__((aligned(8)));

struct bpf_map_info {
        __u32 type;
        __u32 id;
        __u32 key_size;
        __u32 value_size;
        __u32 max_entries;
        __u32 map_flags;
        char  name[BPF_OBJ_NAME_LEN];
        __u32 ifindex;
        __u32 :32;
        __u64 netns_dev;
        __u64 netns_ino;
        __u32 btf_id;
        __u32 btf_key_type_id;
        __u32 btf_value_type_id;
} __attribute__((aligned(8)));

struct bpf_btf_info {
        __aligned_u64 btf;
        __u32 btf_size;
        __u32 id;
} __attribute__((aligned(8)));

/* User bpf_sock_addr struct to access socket fields and sockaddr struct passed
 * by user and intended to be used by socket (e.g. to bind to, depends on
 * attach attach type).
 */
struct bpf_sock_addr {
        __u32 user_family;      /* Allows 4-byte read, but no write. */
        __u32 user_ip4;         /* Allows 1,2,4-byte read and 4-byte write.
                                 * Stored in network byte order.
                                 */
        __u32 user_ip6[4];      /* Allows 1,2,4,8-byte read and 4,8-byte write.
                                 * Stored in network byte order.
                                 */
        __u32 user_port;        /* Allows 4-byte read and write.
                                 * Stored in network byte order
                                 */
        __u32 family;           /* Allows 4-byte read, but no write */
        __u32 type;             /* Allows 4-byte read, but no write */
        __u32 protocol;         /* Allows 4-byte read, but no write */
        __u32 msg_src_ip4;      /* Allows 1,2,4-byte read and 4-byte write.
                                 * Stored in network byte order.
                                 */
        __u32 msg_src_ip6[4];   /* Allows 1,2,4,8-byte read and 4,8-byte write.
                                 * Stored in network byte order.
                                 */
        __bpf_md_ptr(struct bpf_sock *, sk);
};

/* User bpf_sock_ops struct to access socket values and specify request ops
 * and their replies.
 * Some of this fields are in network (bigendian) byte order and may need
 * to be converted before use (bpf_ntohl() defined in samples/bpf/bpf_endian.h).
 * New fields can only be added at the end of this structure
 */
struct bpf_sock_ops {
        __u32 op;
        union {
                __u32 args[4];          /* Optionally passed to bpf program */
                __u32 reply;            /* Returned by bpf program          */
                __u32 replylong[4];     /* Optionally returned by bpf prog  */
        };
        __u32 family;
        __u32 remote_ip4;       /* Stored in network byte order */
        __u32 local_ip4;        /* Stored in network byte order */
        __u32 remote_ip6[4];    /* Stored in network byte order */
        __u32 local_ip6[4];     /* Stored in network byte order */
        __u32 remote_port;      /* Stored in network byte order */
        __u32 local_port;       /* stored in host byte order */
        __u32 is_fullsock;      /* Some TCP fields are only valid if
                                 * there is a full socket. If not, the
                                 * fields read as zero.
                                 */
        __u32 snd_cwnd;
        __u32 srtt_us;          /* Averaged RTT << 3 in usecs */
        __u32 bpf_sock_ops_cb_flags; /* flags defined in uapi/linux/tcp.h */
        __u32 state;
        __u32 rtt_min;
        __u32 snd_ssthresh;
        __u32 rcv_nxt;
        __u32 snd_nxt;
        __u32 snd_una;
        __u32 mss_cache;
        __u32 ecn_flags;
        __u32 rate_delivered;
        __u32 rate_interval_us;
        __u32 packets_out;
        __u32 retrans_out;
        __u32 total_retrans;
        __u32 segs_in;
        __u32 data_segs_in;
        __u32 segs_out;
        __u32 data_segs_out;
        __u32 lost_out;
        __u32 sacked_out;
        __u32 sk_txhash;
        __u64 bytes_received;
        __u64 bytes_acked;
        __bpf_md_ptr(struct bpf_sock *, sk);
};

/* Definitions for bpf_sock_ops_cb_flags */
#define BPF_SOCK_OPS_RTO_CB_FLAG        (1<<0)
#define BPF_SOCK_OPS_RETRANS_CB_FLAG    (1<<1)
#define BPF_SOCK_OPS_STATE_CB_FLAG      (1<<2)
#define BPF_SOCK_OPS_RTT_CB_FLAG        (1<<3)
#define BPF_SOCK_OPS_ALL_CB_FLAGS       0xF             /* Mask of all currently
                                                         * supported cb flags
                                                         */

/* List of known BPF sock_ops operators.
 * New entries can only be added at the end
 */
enum {
        BPF_SOCK_OPS_VOID,
        BPF_SOCK_OPS_TIMEOUT_INIT,      /* Should return SYN-RTO value to use or
                                         * -1 if default value should be used
                                         */
        BPF_SOCK_OPS_RWND_INIT,         /* Should return initial advertized
                                         * window (in packets) or -1 if default
                                         * value should be used
                                         */
        BPF_SOCK_OPS_TCP_CONNECT_CB,    /* Calls BPF program right before an
                                         * active connection is initialized
                                         */
        BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB,     /* Calls BPF program when an
                                                 * active connection is
                                                 * established
                                                 */
        BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB,    /* Calls BPF program when a
                                                 * passive connection is
                                                 * established
                                                 */
        BPF_SOCK_OPS_NEEDS_ECN,         /* If connection's congestion control
                                         * needs ECN
                                         */
        BPF_SOCK_OPS_BASE_RTT,          /* Get base RTT. The correct value is
                                         * based on the path and may be
                                         * dependent on the congestion control
                                         * algorithm. In general it indicates
                                         * a congestion threshold. RTTs above
                                         * this indicate congestion
                                         */
        BPF_SOCK_OPS_RTO_CB,            /* Called when an RTO has triggered.
                                         * Arg1: value of icsk_retransmits
                                         * Arg2: value of icsk_rto
                                         * Arg3: whether RTO has expired
                                         */
        BPF_SOCK_OPS_RETRANS_CB,        /* Called when skb is retransmitted.
                                         * Arg1: sequence number of 1st byte
                                         * Arg2: # segments
                                         * Arg3: return value of
                                         *       tcp_transmit_skb (0 => success)
                                         */
        BPF_SOCK_OPS_STATE_CB,          /* Called when TCP changes state.
                                         * Arg1: old_state
                                         * Arg2: new_state
                                         */
        BPF_SOCK_OPS_TCP_LISTEN_CB,     /* Called on listen(2), right after
                                         * socket transition to LISTEN state.
                                         */
        BPF_SOCK_OPS_RTT_CB,            /* Called on every RTT.
                                         */
};

/* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
 * changes between the TCP and BPF versions. Ideally this should never happen.
 * If it does, we need to add code to convert them before calling
 * the BPF sock_ops function.
 */
enum {
        BPF_TCP_ESTABLISHED = 1,
        BPF_TCP_SYN_SENT,
        BPF_TCP_SYN_RECV,
        BPF_TCP_FIN_WAIT1,
        BPF_TCP_FIN_WAIT2,
        BPF_TCP_TIME_WAIT,
        BPF_TCP_CLOSE,
        BPF_TCP_CLOSE_WAIT,
        BPF_TCP_LAST_ACK,
        BPF_TCP_LISTEN,
        BPF_TCP_CLOSING,        /* Now a valid state */
        BPF_TCP_NEW_SYN_RECV,

        BPF_TCP_MAX_STATES      /* Leave at the end! */
};

#define TCP_BPF_IW              1001    /* Set TCP initial congestion window */
#define TCP_BPF_SNDCWND_CLAMP   1002    /* Set sndcwnd_clamp */

struct bpf_perf_event_value {
        __u64 counter;
        __u64 enabled;
        __u64 running;
};

#define BPF_DEVCG_ACC_MKNOD     (1ULL << 0)
#define BPF_DEVCG_ACC_READ      (1ULL << 1)
#define BPF_DEVCG_ACC_WRITE     (1ULL << 2)

#define BPF_DEVCG_DEV_BLOCK     (1ULL << 0)
#define BPF_DEVCG_DEV_CHAR      (1ULL << 1)

struct bpf_cgroup_dev_ctx {
        /* access_type encoded as (BPF_DEVCG_ACC_* << 16) | BPF_DEVCG_DEV_* */
        __u32 access_type;
        __u32 major;
        __u32 minor;
};

struct bpf_raw_tracepoint_args {
        __u64 args[0];
};

/* DIRECT:  Skip the FIB rules and go to FIB table associated with device
 * OUTPUT:  Do lookup from egress perspective; default is ingress
 */
#define BPF_FIB_LOOKUP_DIRECT  (1U << 0)
#define BPF_FIB_LOOKUP_OUTPUT  (1U << 1)

enum {
        BPF_FIB_LKUP_RET_SUCCESS,      /* lookup successful */
        BPF_FIB_LKUP_RET_BLACKHOLE,    /* dest is blackholed; can be dropped */
        BPF_FIB_LKUP_RET_UNREACHABLE,  /* dest is unreachable; can be dropped */
        BPF_FIB_LKUP_RET_PROHIBIT,     /* dest not allowed; can be dropped */
        BPF_FIB_LKUP_RET_NOT_FWDED,    /* packet is not forwarded */
        BPF_FIB_LKUP_RET_FWD_DISABLED, /* fwding is not enabled on ingress */
        BPF_FIB_LKUP_RET_UNSUPP_LWT,   /* fwd requires encapsulation */
        BPF_FIB_LKUP_RET_NO_NEIGH,     /* no neighbor entry for nh */
        BPF_FIB_LKUP_RET_FRAG_NEEDED,  /* fragmentation required to fwd */
};

struct bpf_fib_lookup {
        /* input:  network family for lookup (AF_INET, AF_INET6)
         * output: network family of egress nexthop
         */
        __u8    family;

        /* set if lookup is to consider L4 data - e.g., FIB rules */
        __u8    l4_protocol;
        __be16  sport;
        __be16  dport;

        /* total length of packet from network header - used for MTU check */
        __u16   tot_len;

        /* input: L3 device index for lookup
         * output: device index from FIB lookup
         */
        __u32   ifindex;

        union {
                /* inputs to lookup */
                __u8    tos;            /* AF_INET  */
                __be32  flowinfo;       /* AF_INET6, flow_label + priority */

                /* output: metric of fib result (IPv4/IPv6 only) */
                __u32   rt_metric;
        };

        union {
                __be32          ipv4_src;
                __u32           ipv6_src[4];  /* in6_addr; network order */
        };

        /* input to bpf_fib_lookup, ipv{4,6}_dst is destination address in
         * network header. output: bpf_fib_lookup sets to gateway address
         * if FIB lookup returns gateway route
         */
        union {
                __be32          ipv4_dst;
                __u32           ipv6_dst[4];  /* in6_addr; network order */
        };

        /* output */
        __be16  h_vlan_proto;
        __be16  h_vlan_TCI;
        __u8    smac[6];     /* ETH_ALEN */
        __u8    dmac[6];     /* ETH_ALEN */
};

enum bpf_task_fd_type {
        BPF_FD_TYPE_RAW_TRACEPOINT,     /* tp name */
        BPF_FD_TYPE_TRACEPOINT,         /* tp name */
        BPF_FD_TYPE_KPROBE,             /* (symbol + offset) or addr */
        BPF_FD_TYPE_KRETPROBE,          /* (symbol + offset) or addr */
        BPF_FD_TYPE_UPROBE,             /* filename + offset */
        BPF_FD_TYPE_URETPROBE,          /* filename + offset */
};

#define BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG             (1U << 0)
#define BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL         (1U << 1)
#define BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP              (1U << 2)

struct bpf_flow_keys {
        __u16   nhoff;
        __u16   thoff;
        __u16   addr_proto;                     /* ETH_P_* of valid addrs */
        __u8    is_frag;
        __u8    is_first_frag;
        __u8    is_encap;
        __u8    ip_proto;
        __be16  n_proto;
        __be16  sport;
        __be16  dport;
        union {
                struct {
                        __be32  ipv4_src;
                        __be32  ipv4_dst;
                };
                struct {
                        __u32   ipv6_src[4];    /* in6_addr; network order */
                        __u32   ipv6_dst[4];    /* in6_addr; network order */
                };
        };
        __u32   flags;
        __be32  flow_label;
};

struct bpf_func_info {
        __u32   insn_off;
        __u32   type_id;
};

#define BPF_LINE_INFO_LINE_NUM(line_col)        ((line_col) >> 10)
#define BPF_LINE_INFO_LINE_COL(line_col)        ((line_col) & 0x3ff)

struct bpf_line_info {
        __u32   insn_off;
        __u32   file_name_off;
        __u32   line_off;
        __u32   line_col;
};

struct bpf_spin_lock {
        __u32   val;
};

struct bpf_sysctl {
        __u32   write;          /* Sysctl is being read (= 0) or written (= 1).
                                 * Allows 1,2,4-byte read, but no write.
                                 */
        __u32   file_pos;       /* Sysctl file position to read from, write to.
                                 * Allows 1,2,4-byte read an 4-byte write.
                                 */
};

struct bpf_sockopt {
        __bpf_md_ptr(struct bpf_sock *, sk);
        __bpf_md_ptr(void *, optval);
        __bpf_md_ptr(void *, optval_end);

        __s32   level;
        __s32   optname;
        __s32   optlen;
        __s32   retval;
};

#endif /* _UAPI__LINUX_BPF_H__ */