On Thu, Feb 17, 2022 at 11:51 PM Dmitrii Dolgov <9erthalion6@xxxxxxxxx> wrote:
>
> 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@xxxxxxxxx>
> ---
> Changes in v3:
> - Use pid iterator to fetch bpf_cookie
>
> Changes in v2:
> - Display bpf_cookie in bpftool link command instead perf
>
> Previous discussion: https://lore.kernel.org/bpf/20220204181146.8429-1-9erthalion6@xxxxxxxxx/
>
> tools/bpf/bpftool/main.h | 2 ++
> tools/bpf/bpftool/pids.c | 15 +++++++++++++--
> tools/bpf/bpftool/skeleton/pid_iter.bpf.c | 16 ++++++++++++++++
> tools/bpf/bpftool/skeleton/pid_iter.h | 1 +
> 4 files changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
> index 0c3840596b5a..c0042bd56139 100644
> --- a/tools/bpf/bpftool/main.h
> +++ b/tools/bpf/bpftool/main.h
> @@ -114,6 +114,8 @@ struct obj_ref {
> struct obj_refs {
> int ref_cnt;
> struct obj_ref *refs;
> + enum bpf_obj_type type;
> + __u64 bpf_cookie;
> };
>
> struct btf;
> diff --git a/tools/bpf/bpftool/pids.c b/tools/bpf/bpftool/pids.c
> index 7c384d10e95f..d4db4049d94b 100644
> --- a/tools/bpf/bpftool/pids.c
> +++ b/tools/bpf/bpftool/pids.c
> @@ -28,7 +28,8 @@ void emit_obj_refs_json(struct hashmap *map, __u32 id, json_writer_t *json_write
>
> #include "pid_iter.skel.h"
>
> -static void add_ref(struct hashmap *map, struct pid_iter_entry *e)
> +static void add_ref(struct hashmap *map, struct pid_iter_entry *e,
> + enum bpf_obj_type type)
> {
> struct hashmap_entry *entry;
> struct obj_refs *refs;
> @@ -55,6 +56,8 @@ 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++;
> + refs->type = type;
> + refs->bpf_cookie = e->bpf_cookie;
>
> return;
> }
> @@ -78,6 +81,8 @@ 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->type = type;
> + refs->bpf_cookie = e->bpf_cookie;
>
> err = hashmap__append(map, u32_as_hash_field(e->id), refs);
> if (err)
> @@ -161,7 +166,7 @@ int build_obj_refs_table(struct hashmap **map, enum bpf_obj_type type)
>
> e = (void *)buf;
> for (i = 0; i < ret; i++, e++) {
> - add_ref(*map, e);
> + add_ref(*map, e, type);
> }
> }
> err = 0;
> @@ -205,6 +210,9 @@ void emit_obj_refs_json(struct hashmap *map, __u32 id,
> if (refs->ref_cnt == 0)
> break;
>
> + if (refs->type == BPF_OBJ_LINK)
> + 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 +242,9 @@ void emit_obj_refs_plain(struct hashmap *map, __u32 id, const char *prefix)
> if (refs->ref_cnt == 0)
> break;
>
> + if (refs->type == BPF_OBJ_LINK)
> + printf("\n\tbpf_cookie %llu", 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 f70702fcb224..afdfdfbf305d 100644
> --- 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)
> }
> }
>
> +static __always_inline __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);
not every bpf_link is bpf_perf_link, you can't do it for every
instance of bpf_link.
> +}
> +
> +
> SEC("iter/task_file")
> int iter(struct bpf_iter__task_file *ctx)
> {
> @@ -71,6 +82,11 @@ int iter(struct bpf_iter__task_file *ctx)
>
> e.pid = task->tgid;
> e.id = get_obj_id(file->private_data, obj_type);
> + e.bpf_cookie = 0;
> +
> + if (obj_type == BPF_OBJ_LINK)
> + e.bpf_cookie = get_bpf_cookie((struct bpf_link *) file->private_data);
> +
> 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 5692cf257adb..a631640f6fe4 100644
> --- a/tools/bpf/bpftool/skeleton/pid_iter.h
> +++ b/tools/bpf/bpftool/skeleton/pid_iter.h
> @@ -7,6 +7,7 @@ struct pid_iter_entry {
> __u32 id;
> int pid;
> char comm[16];
> + __u64 bpf_cookie;
> };
>
> #endif
> --
> 2.32.0
>
