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bpftool: Add bpf_cookie to link output

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Commit 82e6b1eee6 ("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
This commit is contained in:
Dmitrii Dolgov 2022-03-09 17:31:12 +01:00 committed by Andrii Nakryiko
parent f98d6dd1e7
commit cbdaf71f7e
4 changed files with 34 additions and 0 deletions
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2
tools/bpf/bpftool/main.h
View File

@ -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;

8
tools/bpf/bpftool/pids.c
View File

@ -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];

22
tools/bpf/bpftool/skeleton/pid_iter.bpf.c
View File

@ -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));

2
tools/bpf/bpftool/skeleton/pid_iter.h
View File

@ -6,6 +6,8 @@
struct pid_iter_entry {
__u32 id;
int pid;
__u64 bpf_cookie;
bool has_bpf_cookie;
char comm[16];
};