libbpf: Expose libbpf ringbufer epoll_fd

This provides a convenient perf ringbuf -> libbpf ringbuf migration
path for users of external polling systems. It is analogous to
perf_buffer__epoll_fd.

Signed-off-by: Brendan Jackman <[email protected]>

Author: bjackman

tools/lib/bpf/libbpf.h

@@ -536,6 +536,7 @@ LIBBPF_API int ring_buffer__add(struct ring_buffer *rb, int map_fd,
 				ring_buffer_sample_fn sample_cb, void *ctx);
 LIBBPF_API int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms);
 LIBBPF_API int ring_buffer__consume(struct ring_buffer *rb);
+LIBBPF_API int ring_buffer__epoll_fd(struct ring_buffer *rb);
 
 /* Perf buffer APIs */
 struct perf_buffer;

tools/lib/bpf/libbpf.map

@@ -348,4 +348,5 @@ LIBBPF_0.3.0 {
 		btf__new_split;
 		xsk_setup_xdp_prog;
 		xsk_socket__update_xskmap;
+                ring_buffer__epoll_fd;
 } LIBBPF_0.2.0;

tools/lib/bpf/ringbuf.c

@@ -282,3 +282,9 @@ int ring_buffer__poll(struct ring_buffer *rb, int timeout_ms)
 	}
 	return cnt < 0 ? -errno : res;
 }
+
+/* Get an fd that can be used to sleep until data is available in the ring(s) */
+int ring_buffer__epoll_fd(struct ring_buffer *rb)
+{
+	return rb->epoll_fd;
+}