On Tue, Apr 12, 2022 at 9:56 AM Kui-Feng Lee <kuifeng@xxxxxx> wrote:
>
> Add a cookie field to the attributes of bpf_link_create().
> Add bpf_program__attach_trace_opts() to attach a cookie to a link.
>
> Signed-off-by: Kui-Feng Lee <kuifeng@xxxxxx>
> ---
Please stick to "libbpf: " prefix for patch subject, we don't use "lib/bpf: "
> tools/lib/bpf/bpf.c | 7 +++++++
> tools/lib/bpf/bpf.h | 3 +++
> tools/lib/bpf/libbpf.c | 33 +++++++++++++++++++++++++++++++++
> tools/lib/bpf/libbpf.h | 12 ++++++++++++
> tools/lib/bpf/libbpf.map | 1 +
> 5 files changed, 56 insertions(+)
>
> diff --git a/tools/lib/bpf/bpf.c b/tools/lib/bpf/bpf.c
> index cf27251adb92..c2454979c3c4 100644
> --- a/tools/lib/bpf/bpf.c
> +++ b/tools/lib/bpf/bpf.c
> @@ -863,6 +863,13 @@ int bpf_link_create(int prog_fd, int target_fd,
> if (!OPTS_ZEROED(opts, kprobe_multi))
> return libbpf_err(-EINVAL);
> break;
> + case BPF_TRACE_FENTRY:
> + case BPF_TRACE_FEXIT:
> + case BPF_MODIFY_RETURN:
> + attr.link_create.tracing.bpf_cookie = OPTS_GET(opts, tracing.bpf_cookie, 0);
> + if (!OPTS_ZEROED(opts, tracing))
> + return libbpf_err(-EINVAL);
> + break;
> default:
> if (!OPTS_ZEROED(opts, flags))
> return libbpf_err(-EINVAL);
> diff --git a/tools/lib/bpf/bpf.h b/tools/lib/bpf/bpf.h
> index f4b4afb6d4ba..4cdbabcccefc 100644
> --- a/tools/lib/bpf/bpf.h
> +++ b/tools/lib/bpf/bpf.h
> @@ -410,6 +410,9 @@ struct bpf_link_create_opts {
> __u32 iter_info_len;
> __u32 target_btf_id;
> union {
> + struct {
> + __u64 bpf_cookie;
> + } tracing;
> struct {
> __u64 bpf_cookie;
> } perf_event;
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index bf4f7ac54ebf..8586e1efd780 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -11262,6 +11262,39 @@ struct bpf_link *bpf_program__attach_trace(const struct bpf_program *prog)
> return bpf_program__attach_btf_id(prog);
> }
>
> +struct bpf_link *bpf_program__attach_trace_opts(const struct bpf_program *prog,
> + const struct bpf_trace_opts *opts)
> +{
> + char errmsg[STRERR_BUFSIZE];
> + struct bpf_link *link;
> + int prog_fd, pfd;
> +
unnecessary empty line, LIBBPF_OPTS is a variable declaration, so keep
it together with other variables
> + LIBBPF_OPTS(bpf_link_create_opts, link_opts);
> +
> + prog_fd = bpf_program__fd(prog);
> + if (prog_fd < 0) {
> + pr_warn("prog '%s': can't attach before loaded\n", prog->name);
> + return libbpf_err_ptr(-EINVAL);
> + }
> +
> + link = calloc(1, sizeof(*link));
> + if (!link)
> + return libbpf_err_ptr(-ENOMEM);
> + link->detach = &bpf_link__detach_fd;
> +
> + link_opts.tracing.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);
> + pfd = bpf_link_create(prog_fd, 0, prog->expected_attach_type, &link_opts);
so this won't work on old kernels that don't support creating
fentry/fexit links through LINK_CREATE. Let's for now check if
bpf_cookie is zero, then redirect to bpf_program__attach_trace().
Ideally we should perform feature detection of ability to use
LINK_CREATE to attach fentry and have a unified single
bpf_program__attach_btf_id() implementation that will handle all that
internally
> + if (pfd < 0) {
> + pfd = -errno;
> + free(link);
> + pr_warn("prog '%s': failed to attach: %s\n",
> + prog->name, libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
> + return libbpf_err_ptr(pfd);
> + }
> + link->fd = pfd;
> + return (struct bpf_link *)link;
> +}
> +
> struct bpf_link *bpf_program__attach_lsm(const struct bpf_program *prog)
> {
> return bpf_program__attach_btf_id(prog);
> diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
> index 63d66f1adf1a..e0dd3f9a5aca 100644
> --- a/tools/lib/bpf/libbpf.h
> +++ b/tools/lib/bpf/libbpf.h
> @@ -563,8 +563,20 @@ bpf_program__attach_tracepoint_opts(const struct bpf_program *prog,
> LIBBPF_API struct bpf_link *
> bpf_program__attach_raw_tracepoint(const struct bpf_program *prog,
> const char *tp_name);
> +
> +struct bpf_trace_opts {
> + /* size of this struct, for forward/backward compatibility */
> + size_t sz;
> + /* custom user-provided value fetchable through bpf_get_attach_cookie() */
> + __u64 bpf_cookie;
> +};
> +#define bpf_trace_opts__last_field bpf_cookie
> +
> LIBBPF_API struct bpf_link *
> bpf_program__attach_trace(const struct bpf_program *prog);
> +LIBBPF_API struct bpf_link *
> +bpf_program__attach_trace_opts(const struct bpf_program *prog, const struct bpf_trace_opts *opts);
> +
> LIBBPF_API struct bpf_link *
> bpf_program__attach_lsm(const struct bpf_program *prog);
> LIBBPF_API struct bpf_link *
> diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
> index 82f6d62176dd..9235da802e31 100644
> --- a/tools/lib/bpf/libbpf.map
> +++ b/tools/lib/bpf/libbpf.map
> @@ -424,6 +424,7 @@ LIBBPF_0.6.0 {
> LIBBPF_0.7.0 {
> global:
> bpf_btf_load;
> + bpf_program__attach_trace_opts;
this should go into LIBBPF_0.8.0
> bpf_program__expected_attach_type;
> bpf_program__log_buf;
> bpf_program__log_level;
> --
> 2.30.2
>
