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Message-ID: <20190621000704.GC1383@mini-arch>
Date: Thu, 20 Jun 2019 17:07:04 -0700
From: Stanislav Fomichev <sdf@...ichev.me>
To: Andrii Nakryiko <andriin@...com>
Cc: andrii.nakryiko@...il.com, ast@...com, daniel@...earbox.net,
netdev@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH bpf-next 4/7] libbpf: add tracepoint/raw tracepoint
attach API
On 06/20, Andrii Nakryiko wrote:
> Add APIs allowing to attach BPF program to kernel tracepoints. Raw
> tracepoint attach API is also added for uniform per-BPF-program API,
> but is mostly a wrapper around existing bpf_raw_tracepoint_open call.
>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
> tools/lib/bpf/libbpf.c | 99 ++++++++++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf.h | 5 ++
> tools/lib/bpf/libbpf.map | 2 +
> 3 files changed, 106 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 11329e05530e..cefe67ba160b 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4176,6 +4176,105 @@ int bpf_program__attach_uprobe(struct bpf_program *prog, bool retprobe,
> return pfd;
> }
>
> +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_uint_from_file(file);
> +}
> +
> +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);
Why no assign to attr.config directly here?
You can move all other constants to the initialization as well:
struct perf_event_attr attr = {
.type = PERF_TYPE_TRACEPON,
.size = sizeof(struct perf_event_attr),
};
attr.config = determine_tracepoint_id(...);
(I guess that's a matter of style, but something to consider).
> + if (tp_id < 0){
> + pr_warning("failed to determine tracepoint '%s/%s' perf ID: %s\n",
> + tp_category, tp_name,
> + libbpf_strerror_r(tp_id, errmsg, sizeof(errmsg)));
> + return tp_id;
> + }
> +
[..]
> + memset(&attr, 0, sizeof(attr));
Not needed since you do attr = {}; above?
> + 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;
> +}
> +
> +int bpf_program__attach_tracepoint(struct bpf_program *prog,
> + const char *tp_category,
> + const char *tp_name)
> +{
> + char errmsg[STRERR_BUFSIZE];
> + 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 pfd;
> + }
> + err = bpf_program__attach_perf_event(prog, pfd);
> + if (err) {
> + libbpf_perf_event_disable_and_close(pfd);
> + 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 err;
> + }
> + return pfd;
> +}
> +
> +int bpf_program__attach_raw_tracepoint(struct bpf_program *prog,
> + const char *tp_name)
> +{
> + char errmsg[STRERR_BUFSIZE];
> + int bpf_fd, pfd;
> +
> + bpf_fd = bpf_program__fd(prog);
> + if (bpf_fd < 0) {
> + pr_warning("program '%s': can't attach before loaded\n",
> + bpf_program__title(prog, false));
> + return -EINVAL;
> + }
> + pfd = bpf_raw_tracepoint_open(tp_name, bpf_fd);
> + if (pfd < 0) {
> + pr_warning("program '%s': failed to attach to raw tracepoint '%s': %s\n",
> + bpf_program__title(prog, false), tp_name,
> + libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
> + return pfd;
> + }
> + return pfd;
> +}
> +
> 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 a7264f06aa5f..bf7020a565c6 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -176,6 +176,11 @@ LIBBPF_API int bpf_program__attach_uprobe(struct bpf_program *prog,
> pid_t pid,
> const char *binary_path,
> size_t func_offset);
> +LIBBPF_API int bpf_program__attach_tracepoint(struct bpf_program *prog,
> + const char *tp_category,
> + const char *tp_name);
> +LIBBPF_API int bpf_program__attach_raw_tracepoint(struct bpf_program *prog,
> + const char *tp_name);
>
> struct bpf_insn;
>
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 1a982c2e1751..2382fbda4cbb 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -174,6 +174,8 @@ LIBBPF_0.0.4 {
> bpf_object__load_xattr;
> bpf_program__attach_kprobe;
> bpf_program__attach_perf_event;
> + bpf_program__attach_raw_tracepoint;
> + bpf_program__attach_tracepoint;
> bpf_program__attach_uprobe;
> libbpf_num_possible_cpus;
> libbpf_perf_event_disable_and_close;
> --
> 2.17.1
>
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