[PATCH bpf-next v2] libbpf: add API to consume the perf ring buffer content

[Eelco Chaudron]

This new API, perf_buffer__consume, can be used as follows:
- When you have a perf ring where wakeup_events is higher than 1,
  and you have remaining data in the rings you would like to pull
  out on exit (or maybe based on a timeout).
- For low latency cases where you burn a CPU that constantly polls
  the queues.

Signed-off-by: Eelco Chaudron <echau...@redhat.com>
---
v2:
 - Removed some input checks
 - Support spare CPU buffers
 - Moved variable "err" up

 tools/lib/bpf/libbpf.c   |   19 +++++++++++++++++++
 tools/lib/bpf/libbpf.h   |    1 +
 tools/lib/bpf/libbpf.map |    1 +
 3 files changed, 21 insertions(+)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index fa04cbe547ed..5d60de6fd818 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8456,6 +8456,25 @@ int perf_buffer__poll(struct perf_buffer *pb, int 
timeout_ms)
        return cnt < 0 ? -errno : cnt;
 }
 
+int perf_buffer__consume(struct perf_buffer *pb)
+{
+       int i, err;
+
+       for (i = 0; i < pb->cpu_cnt; i++) {
+               struct perf_cpu_buf *cpu_buf = pb->cpu_bufs[i];
+
+               if (!cpu_buf)
+                       continue;
+
+               err = perf_buffer__process_records(pb, cpu_buf);
+               if (err) {
+                       pr_warn("error while processing records: %d\n", err);
+                       return err;
+               }
+       }
+       return 0;
+}
+
 struct bpf_prog_info_array_desc {
        int     array_offset;   /* e.g. offset of jited_prog_insns */
        int     count_offset;   /* e.g. offset of jited_prog_len */
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 8ea69558f0a8..1e2e399a5f2c 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -533,6 +533,7 @@ perf_buffer__new_raw(int map_fd, size_t page_cnt,
 
 LIBBPF_API void perf_buffer__free(struct perf_buffer *pb);
 LIBBPF_API int perf_buffer__poll(struct perf_buffer *pb, int timeout_ms);
+LIBBPF_API int perf_buffer__consume(struct perf_buffer *pb);
 
 typedef enum bpf_perf_event_ret
        (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 0133d469d30b..381a7342ecfc 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -262,4 +262,5 @@ LIBBPF_0.0.9 {
                bpf_link_get_fd_by_id;
                bpf_link_get_next_id;
                bpf_program__attach_iter;
+               perf_buffer__consume;
 } LIBBPF_0.0.8;