trace_helpers.c: Add helpers to poll multiple perf FDs for events

Add two new helper functions to trace_helpers that supports polling
multiple perf file descriptors for events. These are used to the XDP
perf_event_output example, which needs to work with one perf fd per CPU.
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/trace_helpers.c

@@ -88,7 +88,7 @@ static int page_size;
 static int page_cnt = 8;
 static struct perf_event_mmap_page *header;
 
-int perf_event_mmap(int fd)
+int perf_event_mmap_header(int fd, struct perf_event_mmap_page **header)
 {
 	void *base;
 	int mmap_size;
@@ -102,10 +102,15 @@ int perf_event_mmap(int fd)
 		return -1;
 	}
 
-	header = base;
+	*header = base;
 	return 0;
 }
 
+int perf_event_mmap(int fd)
+{
+	return perf_event_mmap_header(fd, &header);
+}
+
 static int perf_event_poll(int fd)
 {
 	struct pollfd pfd = { .fd = fd, .events = POLLIN };
@@ -163,3 +168,42 @@ int perf_event_poller(int fd, perf_event_print_fn output_fn)
 
 	return ret;
 }
+
+int perf_event_poller_multi(int *fds, struct perf_event_mmap_page **headers,
+			    int num_fds, perf_event_print_fn output_fn)
+{
+	enum bpf_perf_event_ret ret;
+	struct pollfd *pfds;
+	void *buf = NULL;
+	size_t len = 0;
+	int i;
+
+	pfds = calloc(num_fds, sizeof(*pfds));
+	if (!pfds)
+		return LIBBPF_PERF_EVENT_ERROR;
+
+	for (i = 0; i < num_fds; i++) {
+		pfds[i].fd = fds[i];
+		pfds[i].events = POLLIN;
+	}
+
+	for (;;) {
+		poll(pfds, num_fds, 1000);
+		for (i = 0; i < num_fds; i++) {
+			if (!pfds[i].revents)
+				continue;
+
+			ret = bpf_perf_event_read_simple(headers[i],
+							 page_cnt * page_size,
+							 page_size, &buf, &len,
+							 bpf_perf_event_print,
+							 output_fn);
+			if (ret != LIBBPF_PERF_EVENT_CONT)
+				break;
+		}
+	}
+	free(buf);
+	free(pfds);
+
+	return ret;
+}

tools/testing/selftests/bpf/trace_helpers.h

@@ -3,6 +3,7 @@
 #define __TRACE_HELPER_H
 
 #include <libbpf.h>
+#include <linux/perf_event.h>
 
 struct ksym {
 	long addr;
@@ -16,6 +17,9 @@ long ksym_get_addr(const char *name);
 typedef enum bpf_perf_event_ret (*perf_event_print_fn)(void *data, int size);
 
 int perf_event_mmap(int fd);
+int perf_event_mmap_header(int fd, struct perf_event_mmap_page **header);
 /* return LIBBPF_PERF_EVENT_DONE or LIBBPF_PERF_EVENT_ERROR */
 int perf_event_poller(int fd, perf_event_print_fn output_fn);
+int perf_event_poller_multi(int *fds, struct perf_event_mmap_page **headers,
+			    int num_fds, perf_event_print_fn output_fn);
 #endif