bpf: Add bpf_link iterator

Implement bpf_link iterator to traverse links via bpf_seq_file
operations. The changeset is mostly shamelessly copied from
commit a228a64fc1e4 ("bpf: Add bpf_prog iterator")

Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20220510155233.9815-2-9erthalion6@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index be94833d390a6cd339a623274a56dafeae9b9ebc..551b7198ae8aff249e8b7bd4b2ff1dd3c248a6dd 100644 (file)
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -1544,6 +1544,7 @@ void bpf_link_put(struct bpf_link *link);
 int bpf_link_new_fd(struct bpf_link *link);
 struct file *bpf_link_new_file(struct bpf_link *link, int *reserved_fd);
 struct bpf_link *bpf_link_get_from_fd(u32 ufd);
+struct bpf_link *bpf_link_get_curr_or_next(u32 *id);
 
 int bpf_obj_pin_user(u32 ufd, const char __user *pathname);
 int bpf_obj_get_user(const char __user *pathname, int flags);

diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index c1a9be6a4b9fab24e0b0c8c4a50c3a73f40f6eab..057ba8e01e70face05b27e845e4c7b09b3e82ed5 100644 (file)
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -6,7 +6,7 @@ cflags-nogcse-$(CONFIG_X86)$(CONFIG_CC_IS_GCC) := -fno-gcse
 endif
 CFLAGS_core.o += $(call cc-disable-warning, override-init) $(cflags-nogcse-yy)
 
-obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o task_iter.o prog_iter.o
+obj-$(CONFIG_BPF_SYSCALL) += syscall.o verifier.o inode.o helpers.o tnum.o bpf_iter.o map_iter.o task_iter.o prog_iter.o link_iter.o
 obj-$(CONFIG_BPF_SYSCALL) += hashtab.o arraymap.o percpu_freelist.o bpf_lru_list.o lpm_trie.o map_in_map.o bloom_filter.o
 obj-$(CONFIG_BPF_SYSCALL) += local_storage.o queue_stack_maps.o ringbuf.o
 obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o

diff --git a/kernel/bpf/link_iter.c b/kernel/bpf/link_iter.c
new file mode 100644 (file)
index 0000000..fec8005
--- /dev/null
+++ b/kernel/bpf/link_iter.c
@@ -0,0 +1,107 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2022 Red Hat, Inc. */
+#include <linux/bpf.h>
+#include <linux/fs.h>
+#include <linux/filter.h>
+#include <linux/kernel.h>
+#include <linux/btf_ids.h>
+
+struct bpf_iter_seq_link_info {
+       u32 link_id;
+};
+
+static void *bpf_link_seq_start(struct seq_file *seq, loff_t *pos)
+{
+       struct bpf_iter_seq_link_info *info = seq->private;
+       struct bpf_link *link;
+
+       link = bpf_link_get_curr_or_next(&info->link_id);
+       if (!link)
+               return NULL;
+
+       if (*pos == 0)
+               ++*pos;
+       return link;
+}
+
+static void *bpf_link_seq_next(struct seq_file *seq, void *v, loff_t *pos)
+{
+       struct bpf_iter_seq_link_info *info = seq->private;
+
+       ++*pos;
+       ++info->link_id;
+       bpf_link_put((struct bpf_link *)v);
+       return bpf_link_get_curr_or_next(&info->link_id);
+}
+
+struct bpf_iter__bpf_link {
+       __bpf_md_ptr(struct bpf_iter_meta *, meta);
+       __bpf_md_ptr(struct bpf_link *, link);
+};
+
+DEFINE_BPF_ITER_FUNC(bpf_link, struct bpf_iter_meta *meta, struct bpf_link *link)
+
+static int __bpf_link_seq_show(struct seq_file *seq, void *v, bool in_stop)
+{
+       struct bpf_iter__bpf_link ctx;
+       struct bpf_iter_meta meta;
+       struct bpf_prog *prog;
+       int ret = 0;
+
+       ctx.meta = &meta;
+       ctx.link = v;
+       meta.seq = seq;
+       prog = bpf_iter_get_info(&meta, in_stop);
+       if (prog)
+               ret = bpf_iter_run_prog(prog, &ctx);
+
+       return ret;
+}
+
+static int bpf_link_seq_show(struct seq_file *seq, void *v)
+{
+       return __bpf_link_seq_show(seq, v, false);
+}
+
+static void bpf_link_seq_stop(struct seq_file *seq, void *v)
+{
+       if (!v)
+               (void)__bpf_link_seq_show(seq, v, true);
+       else
+               bpf_link_put((struct bpf_link *)v);
+}
+
+static const struct seq_operations bpf_link_seq_ops = {
+       .start  = bpf_link_seq_start,
+       .next   = bpf_link_seq_next,
+       .stop   = bpf_link_seq_stop,
+       .show   = bpf_link_seq_show,
+};
+
+BTF_ID_LIST(btf_bpf_link_id)
+BTF_ID(struct, bpf_link)
+
+static const struct bpf_iter_seq_info bpf_link_seq_info = {
+       .seq_ops                = &bpf_link_seq_ops,
+       .init_seq_private       = NULL,
+       .fini_seq_private       = NULL,
+       .seq_priv_size          = sizeof(struct bpf_iter_seq_link_info),
+};
+
+static struct bpf_iter_reg bpf_link_reg_info = {
+       .target                 = "bpf_link",
+       .ctx_arg_info_size      = 1,
+       .ctx_arg_info           = {
+               { offsetof(struct bpf_iter__bpf_link, link),
+                 PTR_TO_BTF_ID_OR_NULL },
+       },
+       .seq_info               = &bpf_link_seq_info,
+};
+
+static int __init bpf_link_iter_init(void)
+{
+       bpf_link_reg_info.ctx_arg_info[0].btf_id = *btf_bpf_link_id;
+       return bpf_iter_reg_target(&bpf_link_reg_info);
+}
+
+late_initcall(bpf_link_iter_init);

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index e0aead17dff48a72486ff3c3d32670ad57e68bdf..50164d324eafc3fa3d719233358e05c355623272 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4680,6 +4680,25 @@ struct bpf_link *bpf_link_by_id(u32 id)
        return link;
 }
 
+struct bpf_link *bpf_link_get_curr_or_next(u32 *id)
+{
+       struct bpf_link *link;
+
+       spin_lock_bh(&link_idr_lock);
+again:
+       link = idr_get_next(&link_idr, id);
+       if (link) {
+               link = bpf_link_inc_not_zero(link);
+               if (IS_ERR(link)) {
+                       (*id)++;
+                       goto again;
+               }
+       }
+       spin_unlock_bh(&link_idr_lock);
+
+       return link;
+}
+
 #define BPF_LINK_GET_FD_BY_ID_LAST_FIELD link_id
 
 static int bpf_link_get_fd_by_id(const union bpf_attr *attr)