netdev - Re: [PATCH v4 bpf-next 6/9] libbpf: add raw tracepoint attach API

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Date:   Mon, 1 Jul 2019 17:13:19 +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 6/9] libbpf: add raw tracepoint attach API



On 6/28/19 8:49 PM, Andrii Nakryiko wrote:
> Add a wrapper utilizing bpf_link "infrastructure" to allow attaching BPF
> programs to raw tracepoints.
> 
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> Acked-by: Song Liu <songliubraving@...com>
> ---
>   tools/lib/bpf/libbpf.c   | 37 +++++++++++++++++++++++++++++++++++++
>   tools/lib/bpf/libbpf.h   |  3 +++
>   tools/lib/bpf/libbpf.map |  1 +
>   3 files changed, 41 insertions(+)
> 
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 8ad4f915df38..f8c7a7ecb35e 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -4263,6 +4263,43 @@ struct bpf_link *bpf_program__attach_tracepoint(struct bpf_program *prog,
>   	return link;
>   }
>   
> +static int bpf_link__destroy_fd(struct bpf_link *link)
> +{
> +	struct bpf_link_fd *l = (void *)link;
> +
> +	return close(l->fd);
> +}
> +
> +struct bpf_link *bpf_program__attach_raw_tracepoint(struct bpf_program *prog,
> +						    const char *tp_name)
> +{
> +	char errmsg[STRERR_BUFSIZE];
> +	struct bpf_link_fd *link;
> +	int prog_fd, pfd;
> +
> +	prog_fd = bpf_program__fd(prog);
> +	if (prog_fd < 0) {
> +		pr_warning("program '%s': can't attach before loaded\n",
> +			   bpf_program__title(prog, false));
> +		return ERR_PTR(-EINVAL);
> +	}
> +
> +	link = malloc(sizeof(*link));
> +	link->link.destroy = &bpf_link__destroy_fd;

You can move the "link = malloc(...)" etc. after 
bpf_raw_tracepoint_open(). That way, you do not need to free(link)
in the error case.

> +
> +	pfd = bpf_raw_tracepoint_open(tp_name, prog_fd);
> +	if (pfd < 0) {
> +		pfd = -errno;
> +		free(link);
> +		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 ERR_PTR(pfd);
> +	}
> +	link->fd = pfd;
> +	return (struct bpf_link *)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 60611f4b4e1d..f55933784f95 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -182,6 +182,9 @@ LIBBPF_API struct bpf_link *
>   bpf_program__attach_tracepoint(struct bpf_program *prog,
>   			       const char *tp_category,
>   			       const char *tp_name);
> +LIBBPF_API struct bpf_link *
> +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 3c618b75ef65..e6b7d4edbc93 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_raw_tracepoint;
>   		bpf_program__attach_tracepoint;
>   		bpf_program__attach_uprobe;
>   		btf_dump__dump_type;
>