[PATCH bpf-next v5 1/2] trace_helpers.c: Add helpers to poll multiple perf FDs for events

[Toke Høiland-Jørgensen]

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.

Signed-off-by: Toke Høiland-Jørgensen <t...@toke.dk>
---
 tools/testing/selftests/bpf/trace_helpers.c |   49 ++++++++++++++++++++++++++-
 tools/testing/selftests/bpf/trace_helpers.h |    4 ++
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/trace_helpers.c 
b/tools/testing/selftests/bpf/trace_helpers.c
index 3868dcb63420..0673e8840cc8 100644
--- a/tools/testing/selftests/bpf/trace_helpers.c
+++ b/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 +168,43 @@ 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 = malloc(sizeof(*pfds) * num_fds);
+       if (!pfds)
+               return LIBBPF_PERF_EVENT_ERROR;
+
+       memset(pfds, 0, sizeof(*pfds) * num_fds);
+       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;
+}
diff --git a/tools/testing/selftests/bpf/trace_helpers.h 
b/tools/testing/selftests/bpf/trace_helpers.h
index 3b4bcf7f5084..18924f23db1b 100644
--- a/tools/testing/selftests/bpf/trace_helpers.h
+++ b/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