libperf: Add group support to perf_evsel__open()

Add support to set group_fd in perf_evsel__open() and make it follow the
group setup.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Requested-by: Shunsuke Nakamura <nakamura.shun@fujitsu.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20210706151704.73662-7-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/perf/evsel.c

@@ -17,6 +17,7 @@
 #include <linux/string.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
+#include <asm/bug.h>
 
 void perf_evsel__init(struct perf_evsel *evsel, struct perf_event_attr *attr,
 		      int idx)
@@ -76,6 +77,25 @@ sys_perf_event_open(struct perf_event_attr *attr,
 	return syscall(__NR_perf_event_open, attr, pid, cpu, group_fd, flags);
 }
 
+static int get_group_fd(struct perf_evsel *evsel, int cpu, int thread)
+{
+	struct perf_evsel *leader = evsel->leader;
+	int fd;
+
+	if (evsel == leader)
+		return -1;
+
+	/*
+	 * Leader must be already processed/open,
+	 * if not it's a bug.
+	 */
+	BUG_ON(!leader->fd);
+
+	fd = FD(leader, cpu, thread);
+	BUG_ON(fd == -1);
+	return fd;
+}
+
 int perf_evsel__open(struct perf_evsel *evsel, struct perf_cpu_map *cpus,
 		     struct perf_thread_map *threads)
 {
@@ -111,11 +131,13 @@ int perf_evsel__open(struct perf_evsel *evsel, struct perf_cpu_map *cpus,
 
 	for (cpu = 0; cpu < cpus->nr; cpu++) {
 		for (thread = 0; thread < threads->nr; thread++) {
-			int fd;
+			int fd, group_fd;
+
+			group_fd = get_group_fd(evsel, cpu, thread);
 
 			fd = sys_perf_event_open(&evsel->attr,
 						 threads->map[thread].pid,
-						 cpus->map[cpu], -1, 0);
+						 cpus->map[cpu], group_fd, 0);
 
 			if (fd < 0)
 				return -errno;