[PATCH net 2/2] samples/bpf: add error checking for perf ioctl calls in bpf loader

[Yonghong Song]

load_bpf_file() should fail if ioctl with command
PERF_EVENT_IOC_ENABLE and PERF_EVENT_IOC_SET_BPF fails.
When they do fail, proper error messages are printed.

With this change, the below "syscall_tp" run shows that
the maximum number of bpf progs attaching to the same
perf tracepoint is indeed enforced.
  $ ./syscall_tp -i 64
  prog #0: map ids 4 5
  ...
  prog #63: map ids 382 383
  $ ./syscall_tp -i 65
  prog #0: map ids 4 5
  ...
  prog #64: map ids 388 389
  ioctl PERF_EVENT_IOC_SET_BPF failed err Argument list too long

Signed-off-by: Yonghong Song <y...@fb.com>
---
 samples/bpf/bpf_load.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/samples/bpf/bpf_load.c b/samples/bpf/bpf_load.c
index 522ca92..242631a 100644
--- a/samples/bpf/bpf_load.c
+++ b/samples/bpf/bpf_load.c
@@ -193,8 +193,18 @@ static int load_and_attach(const char *event, struct 
bpf_insn *prog, int size)
                return -1;
        }
        event_fd[prog_cnt - 1] = efd;
-       ioctl(efd, PERF_EVENT_IOC_ENABLE, 0);
-       ioctl(efd, PERF_EVENT_IOC_SET_BPF, fd);
+       err = ioctl(efd, PERF_EVENT_IOC_ENABLE, 0);
+       if (err < 0) {
+               printf("ioctl PERF_EVENT_IOC_ENABLE failed err %s\n",
+                      strerror(errno));
+               return -1;
+       }
+       err = ioctl(efd, PERF_EVENT_IOC_SET_BPF, fd);
+       if (err < 0) {
+               printf("ioctl PERF_EVENT_IOC_SET_BPF failed err %s\n",
+                      strerror(errno));
+               return -1;
+       }
 
        return 0;
 }
-- 
2.9.5