[PATCH 4/9] ext4: make __ext4_block_zero_page_range() support large folio

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

The partial block zero range helper __ext4_block_zero_page_range()
currently only supports folios of PAGE_SIZE in size. The calculations
for the start block and the offset within a folio for the given range
are incorrect. Modify the implementation to use offset_in_folio()
instead of directly masking PAGE_SIZE - 1, which will be able to support
for large folios.

Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 fs/ext4/inode.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index b377e9c912b9..38d33569c26e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3659,9 +3659,7 @@ void ext4_set_aops(struct inode *inode)
 static int __ext4_block_zero_page_range(handle_t *handle,
 		struct address_space *mapping, loff_t from, loff_t length)
 {
-	ext4_fsblk_t index = from >> PAGE_SHIFT;
-	unsigned offset = from & (PAGE_SIZE-1);
-	unsigned blocksize, pos;
+	unsigned int offset, blocksize, pos;
 	ext4_lblk_t iblock;
 	struct inode *inode = mapping->host;
 	struct buffer_head *bh;
@@ -3676,13 +3674,14 @@ static int __ext4_block_zero_page_range(handle_t *handle,
 
 	blocksize = inode->i_sb->s_blocksize;
 
-	iblock = index << (PAGE_SHIFT - inode->i_sb->s_blocksize_bits);
+	iblock = folio->index << (PAGE_SHIFT - inode->i_sb->s_blocksize_bits);
 
 	bh = folio_buffers(folio);
 	if (!bh)
 		bh = create_empty_buffers(folio, blocksize, 0);
 
 	/* Find the buffer that contains "offset" */
+	offset = offset_in_folio(folio, from);
 	pos = blocksize;
 	while (offset >= pos) {
 		bh = bh->b_this_page;
-- 
2.46.1