@@ -2477,7 +2477,8 @@ int ext4_ext_writepage_trans_blocks(stru
 /*
  * preallocate space for a file. This implements ext4's fallocate inode
  * operation, which gets called from sys_fallocate system call.
- * Currently only FA_ALLOCATE mode is supported on extent based files.
+ * Currently only FA_ALLOCATE  and FA_RESV_SPACE modes are supported on
+ * extent based files.
  * We may have more modes supported in future - like FA_DEALLOCATE, which
  * tells fallocate to unallocate previously (pre)allocated blocks.
  * For block-mapped files, posix_fallocate should fall back to the method

@@ -2499,7 +2500,8 @@ long ext4_fallocate(struct inode *inode,
 	 * currently supporting (pre)allocate mode for extent-based
 	 * files _only_
 	 */
-	if (mode != FA_ALLOCATE || !(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL))
+	if (!(EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) ||
+		!(mode == FA_ALLOCATE || mode == FA_RESV_SPACE))
 		return -EOPNOTSUPP;
 
 	/* preallocation to directories is currently not supported */

@@ -2572,9 +2574,10 @@ retry:
 
 	/*
 	 * Time to update the file size.
-	 * Update only when preallocation was requested beyond the file size.
+	 * Update only when preallocation was requested beyond the file size
+	 * and when FA_FL_KEEP_SIZE mode is not specified!
 	 */
-	if ((offset + len) > i_size_read(inode)) {
+	if (!(mode & FA_FL_KEEP_SIZE) && (offset + len) > i_size_read(inode)) {
 		if (ret > 0) {
 			/*
 			 * if no error, we assume preallocation succeeded