[PATCH v4 4/9] ext4: move partial block zeroing earlier in ext4_zero_range()

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

In ext4_zero_range(), move the ext4_zero_partial_blocks() call, which
handles unaligned edges, into the same branch where the unaligned range
is preallocated, immediately after ext4_alloc_file_blocks(). This is
safe because there is no dependency between partial block handling and
the subsequent full block handling.

This change will be used by later patches that handle unaligned
FALLOC_FL_WRITE_ZEROES operations, which will need to check the partial
zeroed result.

Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
---
 fs/ext4/extents.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 125f628e738a..27ca641e701b 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4734,10 +4734,16 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 	}
 
 	flags = EXT4_GET_BLOCKS_CREATE_UNWRIT_EXT;
-	/* Preallocate the range including the unaligned edges */
+	/*
+	 * Preallocate the range including the unaligned edges, and zero
+	 * out partial blocks if they already contain data.
+	 */
 	if (!IS_ALIGNED(offset | end, blocksize)) {
 		ret = ext4_alloc_file_blocks(file, offset, len, new_size,
 					     flags);
+		if (!ret)
+			ret = ext4_zero_partial_blocks(inode, offset, len,
+						       &partial_zeroed);
 		if (ret)
 			return ret;
 	}
@@ -4770,10 +4776,6 @@ static long ext4_zero_range(struct file *file, loff_t offset,
 	if (IS_ALIGNED(offset | end, blocksize))
 		return ret;
 
-	/* Zero out partial block at the edges of the range */
-	ret = ext4_zero_partial_blocks(inode, offset, len, &partial_zeroed);
-	if (ret)
-		return ret;
 	if (((file->f_flags & O_SYNC) || IS_SYNC(inode)) && partial_zeroed) {
 		ret = filemap_write_and_wait_range(inode->i_mapping, offset,
 						   end - 1);
-- 
2.52.0