perf cgroup: Add evlist__add_default_cgroup()

So that tools like 'perf trace' can allow the user to set a cgroup
to be used for all the evsels still without a crgroup setup by
parse_cgroups(), such as the one to use for the syscalls, vfs_getname
and other events involved in strace like syscall tracing.

Cc: Adrian Hunter <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Jiri Olsa <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Stephane Eranian <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: https://lkml.kernel.org/n/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/util/cgroup.c

···
        return cgroup;
 }
 
+static void evsel__set_default_cgroup(struct perf_evsel *evsel, struct cgroup *cgroup)
+{
+	if (evsel->cgrp == NULL)
+		evsel->cgrp = cgroup__get(cgroup);
+}
+
+void evlist__set_default_cgroup(struct perf_evlist *evlist, struct cgroup *cgroup)
+{
+	struct perf_evsel *evsel;
+
+	evlist__for_each_entry(evlist, evsel)
+		evsel__set_default_cgroup(evsel, cgroup);
+}
+
 int parse_cgroups(const struct option *opt, const char *str,
 		  int unset __maybe_unused)
 {

tools/perf/util/cgroup.h

···
 
 struct cgroup *evlist__findnew_cgroup(struct perf_evlist *evlist, char *name);
 
+void evlist__set_default_cgroup(struct perf_evlist *evlist, struct cgroup *cgroup);
+
 int parse_cgroups(const struct option *opt, const char *str, int unset);
 
 #endif /* __CGROUP_H__ */