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iomap: account for unaligned end offsets when truncating read range

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The end position to start truncating from may be at an offset into a
block, which under the current logic would result in overtruncation.

Adjust the calculation to account for unaligned end offsets.

Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Link: https://patch.msgid.link/20251111193658.3495942-3-joannelkoong@gmail.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Joanne Koong 2025-11-11 11:36:51 -08:00 committed by Christian Brauner
parent a0f1cabe29
commit 9d875e0eef
No known key found for this signature in database
GPG Key ID: 91C61BC06578DCA2
1 changed files with 20 additions and 2 deletions
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22
fs/iomap/buffered-io.c
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@ -218,6 +218,22 @@ static void ifs_free(struct folio *folio)
kfree(ifs);
}
/*
* Calculate how many bytes to truncate based off the number of blocks to
* truncate and the end position to start truncating from.
*/
static size_t iomap_bytes_to_truncate(loff_t end_pos, unsigned block_bits,
unsigned blocks_truncated)
{
unsigned block_size = 1 << block_bits;
unsigned block_offset = end_pos & (block_size - 1);
if (!block_offset)
return blocks_truncated << block_bits;
return ((blocks_truncated - 1) << block_bits) + block_offset;
}
/*
* Calculate the range inside the folio that we actually need to read.
*/
@ -263,7 +279,8 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
/* truncate len if we find any trailing uptodate block(s) */
while (++i <= last) {
if (ifs_block_is_uptodate(ifs, i)) {
plen -= (last - i + 1) * block_size;
plen -= iomap_bytes_to_truncate(*pos + plen,
block_bits, last - i + 1);
last = i - 1;
break;
}
@ -279,7 +296,8 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio,
unsigned end = offset_in_folio(folio, isize - 1) >> block_bits;
if (first <= end && last > end)
plen -= (last - end) * block_size;
plen -= iomap_bytes_to_truncate(*pos + plen, block_bits,
last - end);
}
*offp = poff;