perf kvm: Move code to generate filename for perf-kvm to function.

The code in builtin-kvm.c to generate filename for perf-kvm is useful to
other command such as builtin-diff.

This patch move the related code form builtin-kvm.c to util/util.c and
wrap them in a function named get_filename_for_perf_kvm.
Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
Link: http://lkml.kernel.org/r/5e09a5c47e8a495e888cbdc65a6fafb2c950f529.1386368672.git.yangds.fnst@cn.fujitsu.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-kvm.c

@@ -1713,12 +1713,7 @@ int cmd_kvm(int argc, const char **argv, const char *prefix __maybe_unused)
 		perf_guest = 1;
 
 	if (!file_name) {
-		if (perf_host && !perf_guest)
-			file_name = strdup("perf.data.host");
-		else if (!perf_host && perf_guest)
-			file_name = strdup("perf.data.guest");
-		else
-			file_name = strdup("perf.data.kvm");
+		file_name = get_filename_for_perf_kvm();
 
 		if (!file_name) {
 			pr_err("Failed to allocate memory for filename\n");

tools/perf/util/util.c

@@ -482,3 +482,17 @@ int filename__read_str(const char *filename, char **buf, size_t *sizep)
 	close(fd);
 	return err;
 }
+
+const char *get_filename_for_perf_kvm(void)
+{
+	const char *filename;
+
+	if (perf_host && !perf_guest)
+		filename = strdup("perf.data.host");
+	else if (!perf_host && perf_guest)
+		filename = strdup("perf.data.guest");
+	else
+		filename = strdup("perf.data.kvm");
+
+	return filename;
+}

tools/perf/util/util.h

@@ -321,4 +321,6 @@ void free_srcline(char *srcline);
 
 int filename__read_int(const char *filename, int *value);
 int filename__read_str(const char *filename, char **buf, size_t *sizep);
+
+const char *get_filename_for_perf_kvm(void);
 #endif /* GIT_COMPAT_UTIL_H */