perf tools: Do not synthesize the treads of default guest.

As the default guest is designed to handle orphan kernel symboles with
--guestkallsysms and --guestmodules, it has no user space.

So we should skip synthesizing threads if machine is default guest.
Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Link: http://lkml.kernel.org/r/e9ddb5dac6f963169657218b12ceb3c2030f54e8.1387572416.git.yangds.fnst@cn.fujitsu.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/event.c

@@ -133,6 +133,9 @@ static pid_t perf_event__synthesize_comm(struct perf_tool *tool,
 		goto out;
 	}
 
+	if (machine__is_default_guest(machine))
+		return 0;
+
 	snprintf(filename, sizeof(filename), "%s/proc/%d/task",
 		 machine->root_dir, pid);
 
@@ -183,6 +186,9 @@ static int perf_event__synthesize_mmap_events(struct perf_tool *tool,
 	FILE *fp;
 	int rc = 0;
 
+	if (machine__is_default_guest(machine))
+		return 0;
+
 	snprintf(filename, sizeof(filename), "%s/proc/%d/maps",
 		 machine->root_dir, pid);
 
@@ -409,6 +415,9 @@ int perf_event__synthesize_threads(struct perf_tool *tool,
 	if (mmap_event == NULL)
 		goto out_free_comm;
 
+	if (machine__is_default_guest(machine))
+		return 0;
+
 	snprintf(proc_path, sizeof(proc_path), "%s/proc", machine->root_dir);
 	proc = opendir(proc_path);