netdev - Re: [PATCH v4 bpf-next 5/9] libbpf: add tracepoint attach API

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Date:   Mon, 1 Jul 2019 17:10:58 +0000
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andriin@...com>,
        "andrii.nakryiko@...il.com" <andrii.nakryiko@...il.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>,
        "sdf@...ichev.me" <sdf@...ichev.me>,
        Song Liu <songliubraving@...com>
Subject: Re: [PATCH v4 bpf-next 5/9] libbpf: add tracepoint attach API



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@...com>
> Acked-by: Song Liu <songliubraving@...com>
> ---
>   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;
>