udf: reduce stack usage of udf_get_filename

Allocate strings with kmalloc.

Checkstack output:
Before: udf_get_filename:          600
After:  udf_get_filename:          136

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/unicode.c

@@ -324,34 +324,43 @@ try_again:
 int udf_get_filename(struct super_block *sb, uint8_t *sname, uint8_t *dname,
 		     int flen)
 {
-	struct ustr filename, unifilename;
-	int len;
+	struct ustr *filename, *unifilename;
+	int len = 0;
 
-	if (udf_build_ustr_exact(&unifilename, sname, flen))
+	filename = kmalloc(sizeof(struct ustr), GFP_NOFS);
+	if (!filename)
 		return 0;
 
+	unifilename = kmalloc(sizeof(struct ustr), GFP_NOFS);
+	if (!unifilename)
+		goto out1;
+
+	if (udf_build_ustr_exact(unifilename, sname, flen))
+		goto out2;
+
 	if (UDF_QUERY_FLAG(sb, UDF_FLAG_UTF8)) {
-		if (!udf_CS0toUTF8(&filename, &unifilename)) {
+		if (!udf_CS0toUTF8(filename, unifilename)) {
 			udf_debug("Failed in udf_get_filename: sname = %s\n",
 				  sname);
-			return 0;
+			goto out2;
 		}
 	} else if (UDF_QUERY_FLAG(sb, UDF_FLAG_NLS_MAP)) {
-		if (!udf_CS0toNLS(UDF_SB(sb)->s_nls_map, &filename,
-				  &unifilename)) {
+		if (!udf_CS0toNLS(UDF_SB(sb)->s_nls_map, filename,
+				  unifilename)) {
 			udf_debug("Failed in udf_get_filename: sname = %s\n",
 				  sname);
-			return 0;
+			goto out2;
 		}
 	} else
-		return 0;
-
-	len = udf_translate_to_linux(dname, filename.u_name, filename.u_len,
-				     unifilename.u_name, unifilename.u_len);
-	if (len)
-		return len;
-
-	return 0;
+		goto out2;
+
+	len = udf_translate_to_linux(dname, filename->u_name, filename->u_len,
+				     unifilename->u_name, unifilename->u_len);
+out2:
+	kfree(unifilename);
+out1:
+	kfree(filename);
+	return len;
 }
 
 int udf_put_filename(struct super_block *sb, const uint8_t *sname,