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iomap: introduce IOMAP_F_ZERO_TAIL flag

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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>
This commit is contained in:
Namjae Jeon 2026-05-18 20:46:55 +09:00 committed by Christian Brauner
parent 47f28b493d
commit 198c3b90e6
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GPG Key ID: 91C61BC06578DCA2
2 changed files with 8 additions and 0 deletions
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4
fs/iomap/buffered-io.c
View File

@ -836,6 +836,7 @@ static int __iomap_write_begin(const struct iomap_iter *iter,
return -EIO;
folio_zero_segments(folio, poff, from, to, poff + plen);
} else {
const struct iomap *iomap = iomap_iter_srcmap(iter);
int status;
if (iter->flags & IOMAP_NOWAIT)
@ -853,6 +854,9 @@ static int __iomap_write_begin(const struct iomap_iter *iter,
len, status, GFP_NOFS);
if (status)
return status;
if (iomap->flags & IOMAP_F_ZERO_TAIL)
folio_zero_segment(folio, to, poff + plen);
}
iomap_set_range_uptodate(folio, poff, plen);
} while ((block_start += plen) < block_end);

4
include/linux/iomap.h
View File

@ -67,6 +67,9 @@ struct vm_fault;
* bio, i.e. set REQ_ATOMIC.
*
* IOMAP_F_INTEGRITY indicates that the filesystems handles integrity metadata.
*
* IOMAP_F_ZERO_TAIL indicates the remainder of the block after the data
* written should be zeroed.
*/
#define IOMAP_F_NEW (1U << 0)
#define IOMAP_F_DIRTY (1U << 1)
@ -86,6 +89,7 @@ struct vm_fault;
#else
#define IOMAP_F_INTEGRITY 0
#endif /* CONFIG_BLK_DEV_INTEGRITY */
#define IOMAP_F_ZERO_TAIL (1U << 10)
/*
* Flag reserved for file system specific usage