[PATCH v2 10/14] fs: iomap: Atomic write support

[John Garry <john.g.garry@oracle.com>]

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 | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 733f83f839b6..197f1bb6a261 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -275,6 +275,7 @@ 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;
 	unsigned int zeroing_size, pad;
@@ -383,6 +384,9 @@ static loff_t iomap_dio_bio_iter(const struct iomap_iter *iter,
 					  GFP_KERNEL);
 		bio->bi_iter.bi_sector = iomap_sector(iomap, pos);
 		bio->bi_ioprio = dio->iocb->ki_ioprio;
+		if (is_atomic)
+			bio->bi_opf |= REQ_ATOMIC;
+
 		bio->bi_private = dio;
 		bio->bi_end_io = iomap_dio_bio_end_io;
 
@@ -399,6 +403,12 @@ 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 */
+			ret = -EINVAL;
+			bio_put(bio);
+			goto out;
+		}
 		if (dio->flags & IOMAP_DIO_WRITE) {
 			task_io_account_write(n);
 		} else {
-- 
2.31.1