On Mon, Jul 1, 2019 at 10:13 AM Yonghong Song [off-list ref] wrote:

On 6/28/19 8:49 PM, Andrii Nakryiko wrote:

quoted

Add a wrapper utilizing bpf_link "infrastructure" to allow attaching BPF
programs to raw tracepoints.

Signed-off-by: Andrii Nakryiko <redacted>
Acked-by: Song Liu <redacted>
---
  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.

It's either `free(link)` here, or `close(pfd)` if malloc fails after
we attached program. Either way extra clean up is needed. I went with
the first one.

quoted

+
+     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;