[PATCH v6 02/13] iomap: comment on atomic write checks in iomap_dio_bio_iter()

John Garry
2025-03-13T17:13:44Z

Help explain the code.

Also clarify the comment for bio size check.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
fs/iomap/direct-io.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 8c1bec473586..9d72b99cb447 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -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 we will submit multiple BIOs, which is
+ * disallowed.
+ */
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.
--
2.31.1