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);
+}
+
+
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
