Commit cbdaf71f authored by Dmitrii Dolgov's avatar Dmitrii Dolgov Committed by Andrii Nakryiko
Browse files

bpftool: Add bpf_cookie to link output 



Commit 82e6b1ee ("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: default avatarDmitrii Dolgov <9erthalion6@gmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Acked-by: default avatarYonghong Song <yhs@fb.com>
Acked-by: default avatarQuentin Monnet <quentin@isovalent.com>
Link: https://lore.kernel.org/bpf/20220309163112.24141-1-9erthalion6@gmail.com
parent f98d6dd1

tools/bpf/bpftool/main.h

+2 −0
Original line number Diff line number Diff line
@@ -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;

tools/bpf/bpftool/pids.c

+8 −0
Original line number Diff line number Diff line
@@ -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];

tools/bpf/bpftool/skeleton/pid_iter.bpf.c

+22 −0
Original line number Diff line number Diff line
@@ -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));

tools/bpf/bpftool/skeleton/pid_iter.h

+2 −0
Original line number Diff line number Diff line
@@ -6,6 +6,8 @@ 
struct pid_iter_entry {

	__u32 id;

	int pid;

	__u64 bpf_cookie;

	bool has_bpf_cookie;

	char comm[16];

};