iomap: introduce IOMAP_F_ZERO_TAIL flag

In filesystems that maintain a separate Valid Data Length, such as exFAT
and NTFS, a partial write may start at or beyond the current valid_size and
extend it. In this case, the region after the previous valid_size but
within the same filesystem block is considered unwritten.

This patch introduces IOMAP_F_ZERO_TAIL. When this flag is set in iomap,
__iomap_write_begin() will zero only the tail portion while preserving any
valid data before it in the same block.

Without this tail zeroing, stale data in the unwritten portion of the block
can remain in the page cache. Subsequent reads can then return incorrect
contents from that region.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Link: https://patch.msgid.link/20260518114705.9601-2-linkinjeon@kernel.org
Acked-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions