perf evlist: Allow reusing the side band thread for more purposes

I.e. so far we had just one event in that side band thread, a dummy one
with attr.bpf_event set, so that 'perf record' can go ahead and ask the
kernel for further information about BPF programs being loaded.

Allow for more than one event to be there, so that we can use it as
well for the upcoming --switch-output-event feature.
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Link: http://lore.kernel.org/lkml/20200429131106.27974-6-acme@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evlist.h

@@ -111,6 +111,7 @@ int perf_evlist__add_sb_event(struct evlist *evlist,
 			      struct perf_event_attr *attr,
 			      perf_evsel__sb_cb_t cb,
 			      void *data);
+void evlist__set_cb(struct evlist *evlist, perf_evsel__sb_cb_t cb, void *data);
 int perf_evlist__start_sb_thread(struct evlist *evlist,
 				 struct target *target);
 void perf_evlist__stop_sb_thread(struct evlist *evlist);

tools/perf/util/sideband_evlist.c

@@ -4,6 +4,7 @@
 #include "util/evlist.h"
 #include "util/evsel.h"
 #include "util/mmap.h"
+#include "util/perf_api_probe.h"
 #include <perf/mmap.h>
 #include <linux/perf_event.h>
 #include <limits.h>
@@ -80,6 +81,19 @@ static void *perf_evlist__poll_thread(void *arg)
 	return NULL;
 }
 
+void evlist__set_cb(struct evlist *evlist, perf_evsel__sb_cb_t cb, void *data)
+{
+	struct evsel *evsel;
+
+	evlist__for_each_entry(evlist, evsel) {
+		evsel->core.attr.sample_id_all    = 1;
+		evsel->core.attr.watermark        = 1;
+		evsel->core.attr.wakeup_watermark = 1;
+		evsel->side_band.cb   = cb;
+		evsel->side_band.data = data;
+      }
+}
+
 int perf_evlist__start_sb_thread(struct evlist *evlist, struct target *target)
 {
 	struct evsel *counter;
@@ -90,6 +104,15 @@ int perf_evlist__start_sb_thread(struct evlist *evlist, struct target *target)
 	if (perf_evlist__create_maps(evlist, target))
 		goto out_delete_evlist;
 
+	if (evlist->core.nr_entries > 1) {
+		bool can_sample_identifier = perf_can_sample_identifier();
+
+		evlist__for_each_entry(evlist, counter)
+			perf_evsel__set_sample_id(counter, can_sample_identifier);
+
+		perf_evlist__set_id_pos(evlist);
+	}
+
 	evlist__for_each_entry(evlist, counter) {
 		if (evsel__open(counter, evlist->core.cpus, evlist->core.threads) < 0)
 			goto out_delete_evlist;