btrfs-progs: introduce test_issubvolname() for simplicity

index 639fb10..b7bfb3e 100644
@@ -43,6 +43,18 @@ static const char * const subvolume_cmd_group_usage[] = {
 };
 
 /*
+ * test if name is a correct subvolume name
+ * this function return
+ * 0-> name is not a correct subvolume name
+ * 1-> name is a correct subvolume name
+ */
+static int test_issubvolname(char *name)
+{
+	return name[0] != '\0' && !strchr(name, '/') &&
+		strcmp(name, ".") && strcmp(name, "..");
+}
+
+/*
  * test if path is a directory
  * this function return
  * 0-> path exists but it is not a directory

@@ -127,8 +139,7 @@ static int cmd_subvol_create(int argc, char **argv)
 	dupdir = strdup(dst);
 	dstdir = dirname(dupdir);
 
-	if (!strcmp(newname, ".") || !strcmp(newname, "..") ||
-	     strchr(newname, '/') ){
+	if (!test_issubvolname(newname)) {
 		fprintf(stderr, "ERROR: uncorrect subvolume name ('%s')\n",
 			newname);
 		goto out;

@@ -302,8 +313,7 @@ again:
 	vname = basename(dupvname);
 	free(cpath);
 
-	if (!strcmp(vname, ".") || !strcmp(vname, "..") ||
-	     strchr(vname, '/')) {
+	if (!test_issubvolname(vname)) {
 		fprintf(stderr, "ERROR: incorrect subvolume name ('%s')\n",
 			vname);
 		ret = 1;

@@ -711,8 +721,7 @@ static int cmd_snapshot(int argc, char **argv)
 		dstdir = dirname(dupdir);
 	}
 
-	if (!strcmp(newname, ".") || !strcmp(newname, "..") ||
-	     strchr(newname, '/') ){
+	if (!test_issubvolname(newname)) {
 		fprintf(stderr, "ERROR: incorrect snapshot name ('%s')\n",
 			newname);
 		goto out;