On 6/28/19 8:49 PM, Andrii Nakryiko wrote:
> Allow attaching BPF programs to kernel tracepoint BPF hooks specified by
> category and name.
>
> Signed-off-by: Andrii Nakryiko <andriin@xxxxxx>
> Acked-by: Song Liu <songliubraving@xxxxxx>
> ---
> tools/lib/bpf/libbpf.c | 79 ++++++++++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf.h | 4 ++
> tools/lib/bpf/libbpf.map | 1 +
> 3 files changed, 84 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 2f79e9563db9..8ad4f915df38 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4184,6 +4184,85 @@ struct bpf_link *bpf_program__attach_uprobe(struct bpf_program *prog,
> return link;
> }
>
> +static int determine_tracepoint_id(const char *tp_category,
> + const char *tp_name)
> +{
> + char file[PATH_MAX];
> + int ret;
> +
> + ret = snprintf(file, sizeof(file),
> + "/sys/kernel/debug/tracing/events/%s/%s/id",
> + tp_category, tp_name);
> + if (ret < 0)
> + return -errno;
> + if (ret >= sizeof(file)) {
> + pr_debug("tracepoint %s/%s path is too long\n",
> + tp_category, tp_name);
> + return -E2BIG;
> + }
> + return parse_value_from_file(file, "%d\n");
> +}
> +
> +static int perf_event_open_tracepoint(const char *tp_category,
> + const char *tp_name)
> +{
> + struct perf_event_attr attr = {};
> + char errmsg[STRERR_BUFSIZE];
> + int tp_id, pfd, err;
> +
> + tp_id = determine_tracepoint_id(tp_category, tp_name);
> + if (tp_id < 0) {
> + pr_warning("failed to determine tracepoint '%s/%s' perf ID: %s\n",
nit: "perf ID" is not accurate. Maybe "event ID" or "perf event ID"?
> + tp_category, tp_name,
> + libbpf_strerror_r(tp_id, errmsg, sizeof(errmsg)));
> + return tp_id;
> + }
> +
> + attr.type = PERF_TYPE_TRACEPOINT;
> + attr.size = sizeof(attr);
> + attr.config = tp_id;
> +
> + pfd = syscall(__NR_perf_event_open, &attr, -1 /* pid */, 0 /* cpu */,
> + -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
> + if (pfd < 0) {
> + err = -errno;
> + pr_warning("tracepoint '%s/%s' perf_event_open() failed: %s\n",
> + tp_category, tp_name,
> + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> + return err;
> + }
> + return pfd;
> +}
> +
> +struct bpf_link *bpf_program__attach_tracepoint(struct bpf_program *prog,
> + const char *tp_category,
> + const char *tp_name)
> +{
> + char errmsg[STRERR_BUFSIZE];
> + struct bpf_link *link;
> + int pfd, err;
> +
> + pfd = perf_event_open_tracepoint(tp_category, tp_name);
> + if (pfd < 0) {
> + pr_warning("program '%s': failed to create tracepoint '%s/%s' perf event: %s\n",
> + bpf_program__title(prog, false),
> + tp_category, tp_name,
> + libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
> + return ERR_PTR(pfd);
> + }
> + link = bpf_program__attach_perf_event(prog, pfd);
> + if (IS_ERR(link)) {
> + close(pfd);
> + err = PTR_ERR(link);
> + pr_warning("program '%s': failed to attach to tracepoint '%s/%s': %s\n",
> + bpf_program__title(prog, false),
> + tp_category, tp_name,
> + libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
> + return link;
> + }
> + return link;
> +}
> +
> enum bpf_perf_event_ret
> bpf_perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
> void **copy_mem, size_t *copy_size,
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index bd767cc11967..60611f4b4e1d 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -178,6 +178,10 @@ LIBBPF_API struct bpf_link *
> bpf_program__attach_uprobe(struct bpf_program *prog, bool retprobe,
> pid_t pid, const char *binary_path,
> size_t func_offset);
> +LIBBPF_API struct bpf_link *
> +bpf_program__attach_tracepoint(struct bpf_program *prog,
> + const char *tp_category,
> + const char *tp_name);
>
> struct bpf_insn;
>
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 57a40fb60718..3c618b75ef65 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -171,6 +171,7 @@ LIBBPF_0.0.4 {
> bpf_object__load_xattr;
> bpf_program__attach_kprobe;
> bpf_program__attach_perf_event;
> + bpf_program__attach_tracepoint;
> bpf_program__attach_uprobe;
> btf_dump__dump_type;
> btf_dump__free;
>
