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iomap: comment on atomic write checks in iomap_dio_bio_iter()

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Help explain the code.

Also clarify the comment for bio size check.

Signed-off-by: John Garry <john.g.garry@oracle.com>
Link: https://lore.kernel.org/r/20250320120250.4087011-3-john.g.garry@oracle.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
John Garry 2025-03-20 12:02:49 +00:00 committed by Christian Brauner
parent d279c80e0b
commit aacd436e40
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1 changed files with 6 additions and 1 deletions
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7
fs/iomap/direct-io.c
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@ -350,6 +350,11 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
bio_opf |= REQ_OP_WRITE;
if (iter->flags & IOMAP_ATOMIC_HW) {
/*
* Ensure that the mapping covers the full write
* length, otherwise it won't be submitted as a single
* bio, which is required to use hardware atomics.
*/
if (length != iter->len)
return -EINVAL;
bio_opf |= REQ_ATOMIC;
@ -449,7 +454,7 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
n = bio->bi_iter.bi_size;
if (WARN_ON_ONCE((bio_opf & REQ_ATOMIC) && n != length)) {
/*
* This bio should have covered the complete length,
* An atomic write bio must cover the complete length,
* which it doesn't, so error. We may need to zero out
* the tail (complete FS block), similar to when
* bio_iov_iter_get_pages() returns an error, above.