From cbdaf71f7e65a45d6e96378ee7bfe3da39c30908 Mon Sep 17 00:00:00 2001 From: Dmitrii Dolgov <9erthalion6@gmail.com> Date: Wed, 9 Mar 2022 17:31:12 +0100 Subject: [PATCH] bpftool: Add bpf_cookie to link output 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@gmail.com> Signed-off-by: Andrii Nakryiko Acked-by: Yonghong Song Acked-by: Quentin Monnet Link: https://lore.kernel.org/bpf/20220309163112.24141-1-9erthalion6@gmail.com --- 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 0468e5b24bd4..6e9277ffc68c 100644 --- a/tools/bpf/bpftool/main.h +++ b/tools/bpf/bpftool/main.h @@ -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; 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]; };