bpftool: Add bpf_cookie to link output

Commit 82e6b1eee6a8 ("bpf: Allow to specify user-provided bpf_cookie for
BPF perf links") introduced the concept of user specified bpf_cookie,
which could be accessed by BPF programs using bpf_get_attach_cookie().
For troubleshooting purposes it is convenient to expose bpf_cookie via
bpftool as well, so there is no need to meddle with the target BPF
program itself.

Implemented using the pid iterator BPF program to actually fetch
bpf_cookies, which allows constraining code changes only to bpftool.

$ bpftool link
1: type 7  prog 5
        bpf_cookie 123
        pids bootstrap(81)

Signed-off-by: Dmitrii Dolgov <9erthalion6@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Acked-by: Quentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20220309163112.24141-1-9erthalion6@gmail.com

diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index 0468e5b24bd46f048c1b05c8c1a0633de38f1c08..6e9277ffc68c096d9e22aaaf2ccc697662831908 100644 (file)
--- a/tools/bpf/bpftool/main.h
+++ b/tools/bpf/bpftool/main.h
@@ -113,7 +113,9 @@ struct obj_ref {
 
 struct obj_refs {
        int ref_cnt;
+       bool has_bpf_cookie;
        struct obj_ref *refs;
+       __u64 bpf_cookie;
 };
 
 struct btf;

diff --git a/tools/bpf/bpftool/pids.c b/tools/bpf/bpftool/pids.c
index 7c384d10e95f83d5dd27e2170867c98717ece58c..bb6c969a114a33b0e50e5b8924550d95f41496af 100644 (file)
--- a/tools/bpf/bpftool/pids.c
+++ b/tools/bpf/bpftool/pids.c
@@ -78,6 +78,8 @@ static void add_ref(struct hashmap *map, struct pid_iter_entry *e)
        ref->pid = e->pid;
        memcpy(ref->comm, e->comm, sizeof(ref->comm));
        refs->ref_cnt = 1;
+       refs->has_bpf_cookie = e->has_bpf_cookie;
+       refs->bpf_cookie = e->bpf_cookie;
 
        err = hashmap__append(map, u32_as_hash_field(e->id), refs);
        if (err)
@@ -205,6 +207,9 @@ void emit_obj_refs_json(struct hashmap *map, __u32 id,
                if (refs->ref_cnt == 0)
                        break;
 
+               if (refs->has_bpf_cookie)
+                       jsonw_lluint_field(json_writer, "bpf_cookie", refs->bpf_cookie);
+
                jsonw_name(json_writer, "pids");
                jsonw_start_array(json_writer);
                for (i = 0; i < refs->ref_cnt; i++) {
@@ -234,6 +239,9 @@ void emit_obj_refs_plain(struct hashmap *map, __u32 id, const char *prefix)
                if (refs->ref_cnt == 0)
                        break;
 
+               if (refs->has_bpf_cookie)
+                       printf("\n\tbpf_cookie %llu", (unsigned long long) refs->bpf_cookie);
+
                printf("%s", prefix);
                for (i = 0; i < refs->ref_cnt; i++) {
                        struct obj_ref *ref = &refs->refs[i];

diff --git a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
index f70702fcb224c35146b242c6635be71da7df409c..eb05ea53afb1269a94e8228d66011967b2d4b2de 100644 (file)
--- a/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
+++ b/tools/bpf/bpftool/skeleton/pid_iter.bpf.c
@@ -38,6 +38,17 @@ static __always_inline __u32 get_obj_id(void *ent, enum bpf_obj_type type)
        }
 }
 
+/* could be used only with BPF_LINK_TYPE_PERF_EVENT links */
+static __u64 get_bpf_cookie(struct bpf_link *link)
+{
+       struct bpf_perf_link *perf_link;
+       struct perf_event *event;
+
+       perf_link = container_of(link, struct bpf_perf_link, link);
+       event = BPF_CORE_READ(perf_link, perf_file, private_data);
+       return BPF_CORE_READ(event, bpf_cookie);
+}
+
 SEC("iter/task_file")
 int iter(struct bpf_iter__task_file *ctx)
 {
@@ -69,8 +80,19 @@ int iter(struct bpf_iter__task_file *ctx)
        if (file->f_op != fops)
                return 0;
 
+       __builtin_memset(&e, 0, sizeof(e));
        e.pid = task->tgid;
        e.id = get_obj_id(file->private_data, obj_type);
+
+       if (obj_type == BPF_OBJ_LINK) {
+               struct bpf_link *link = (struct bpf_link *) file->private_data;
+
+               if (BPF_CORE_READ(link, type) == BPF_LINK_TYPE_PERF_EVENT) {
+                       e.has_bpf_cookie = true;
+                       e.bpf_cookie = get_bpf_cookie(link);
+               }
+       }
+
        bpf_probe_read_kernel_str(&e.comm, sizeof(e.comm),
                                  task->group_leader->comm);
        bpf_seq_write(ctx->meta->seq, &e, sizeof(e));

diff --git a/tools/bpf/bpftool/skeleton/pid_iter.h b/tools/bpf/bpftool/skeleton/pid_iter.h
index 5692cf257adb914e7fdc996a2dce4be0b024aebb..bbb570d4cca696190dc5aaf06ce814097bd2af69 100644 (file)
--- a/tools/bpf/bpftool/skeleton/pid_iter.h
+++ b/tools/bpf/bpftool/skeleton/pid_iter.h
@@ -6,6 +6,8 @@
 struct pid_iter_entry {
        __u32 id;
        int pid;
+       __u64 bpf_cookie;
+       bool has_bpf_cookie;
        char comm[16];
 };