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From: John Garry <john.g.garry@oracle.com>
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        John Garry <john.g.garry@oracle.com>
Subject: [PATCH v4 18/22] iomap: Atomic write support
Date: Fri,  7 Jun 2024 14:39:15 +0000
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Support atomic writes by producing a single BIO with REQ_ATOMIC flag set.

We rely on the FS to guarantee extent alignment, such that an atomic write
should never straddle two or more extents. The FS should also check for
validity of an atomic write length/alignment.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
 fs/iomap/direct-io.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 5be8d886ab4a..4f2a4569aaa7 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -256,7 +256,7 @@ static void iomap_dio_zero(const struct iomap_iter *iter, struct iomap_dio *dio,
  * clearing the WRITE_THROUGH flag in the dio request.
  */
 static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
-		const struct iomap *iomap, bool use_fua)
+		const struct iomap *iomap, bool use_fua, bool is_atomic)
 {
 	blk_opf_t opflags = REQ_SYNC | REQ_IDLE;
 
@@ -268,6 +268,8 @@ static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
 		opflags |= REQ_FUA;
 	else
 		dio->flags &= ~IOMAP_DIO_WRITE_THROUGH;
+	if (is_atomic)
+		opflags |= REQ_ATOMIC;
 
 	return opflags;
 }
@@ -275,6 +277,7 @@ static inline blk_opf_t iomap_dio_bio_opflags(struct iomap_dio *dio,
 static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
 		struct iomap_dio *dio)
 {
+	bool is_atomic = dio->iocb->ki_flags & IOCB_ATOMIC;
 	const struct iomap *iomap = &iter->iomap;
 	struct inode *inode = iter->inode;
 	u64 io_block_size = iomap->io_block_size;
@@ -373,7 +376,7 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
 	 * can set up the page vector appropriately for a ZONE_APPEND
 	 * operation.
 	 */
-	bio_opf = iomap_dio_bio_opflags(dio, iomap, use_fua);
+	bio_opf = iomap_dio_bio_opflags(dio, iomap, use_fua, is_atomic);
 
 	nr_pages = bio_iov_vecs_to_alloc(dio->submit.iter, BIO_MAX_VECS);
 	do {
@@ -406,6 +409,17 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
 		}
 
 		n = bio->bi_iter.bi_size;
+		if (is_atomic && (n != orig_count)) {
+			/*
+			 * This bio should have covered the complete length,
+			 * which it doesn't, so error. We may need to zero out
+			 * the tail, similar to when bio_iov_iter_get_pages()
+			 * returns an error, above.
+			 */
+			ret = -EINVAL;
+			bio_put(bio);
+			goto zero_tail;
+		}
 		if (dio->flags & IOMAP_DIO_WRITE) {
 			task_io_account_write(n);
 		} else {
-- 
2.31.1