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>
Acked-by: Yonghong Song <yhs@xxxxxx>
---
Changes in v6:
- Remove unnecessary initialization of fields in pid_iter_entry
- Changing bpf_cookie_set to has_bpf_cookie
- Small code cleanup (casting bpf_cookie when needed, removing
__always_inline, etc.)
Changes in v5:
- Remove unneeded cookie assigns
Changes in v4:
- Fetch cookies only for bpf_perf_link
- Signal about bpf_cookie via the flag, instead of deducing it from
the object and link type
- Reset pid_iter_entry to avoid invalid indirect read from stack
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/20220225152802.20957-1-9erthalion6@xxxxxxxxx/
tools/bpf/bpftool/main.h | 2 ++
tools/bpf/bpftool/pids.c | 8 ++++++++
tools/bpf/bpftool/skeleton/pid_iter.bpf.c | 22 ++++++++++++++++++++++
tools/bpf/bpftool/skeleton/pid_iter.h | 2 ++
4 files changed, 34 insertions(+)
diff --git a/tools/bpf/bpftool/main.h b/tools/bpf/bpftool/main.h
index 0c3840596b5a..3574bef7d4ce 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;
+ bool has_bpf_cookie;
+ __u64 bpf_cookie;
};
struct btf;
diff --git a/tools/bpf/bpftool/pids.c b/tools/bpf/bpftool/pids.c
index 7c384d10e95f..bb6c969a114a 100644
--- 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 f70702fcb224..eb05ea53afb1 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)
}
}
+/* 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 5692cf257adb..bbb570d4cca6 100644
--- 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];
};
--
2.32.0
