xfs: use bounce buffering direct I/O when the device requires stable pages

Fix direct I/O on devices that require stable pages by asking iomap
to bounce buffer.  To support this, ioends are used for direct reads
in this case to provide a user context for copying data back from the
bounce buffer.

This fixes qemu when used on devices using T10 protection information
and probably other cases like iSCSI using data digests.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Tested-by: Anuj Gupta <anuj20.g@samsung.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Christoph Hellwig

fs/xfs/xfs_aops.c

@@ -103,7 +103,7 @@ xfs_ioend_put_open_zones(
  * IO write completion.
  */
 STATIC void
-xfs_end_ioend(
+xfs_end_ioend_write(
 	struct iomap_ioend	*ioend)
 {
 	struct xfs_inode	*ip = XFS_I(ioend->io_inode);
@@ -202,7 +202,11 @@ xfs_end_io(
 			io_list))) {
 		list_del_init(&ioend->io_list);
 		iomap_ioend_try_merge(ioend, &tmp);
-		xfs_end_ioend(ioend);
+		if (bio_op(&ioend->io_bio) == REQ_OP_READ)
+			iomap_finish_ioends(ioend,
+				blk_status_to_errno(ioend->io_bio.bi_status));
+		else
+			xfs_end_ioend_write(ioend);
 		cond_resched();
 	}
 }

fs/xfs/xfs_file.c

@@ -224,12 +224,34 @@ xfs_ilock_iocb_for_write(
 	return 0;
 }
 
+/*
+ * Bounce buffering dio reads need a user context to copy back the data.
+ * Use an ioend to provide that.
+ */
+static void
+xfs_dio_read_bounce_submit_io(
+	const struct iomap_iter	*iter,
+	struct bio		*bio,
+	loff_t			file_offset)
+{
+	iomap_init_ioend(iter->inode, bio, file_offset, IOMAP_IOEND_DIRECT);
+	bio->bi_end_io = xfs_end_bio;
+	submit_bio(bio);
+}
+
+static const struct iomap_dio_ops xfs_dio_read_bounce_ops = {
+	.submit_io	= xfs_dio_read_bounce_submit_io,
+	.bio_set	= &iomap_ioend_bioset,
+};
+
 STATIC ssize_t
 xfs_file_dio_read(
 	struct kiocb		*iocb,
 	struct iov_iter		*to)
 {
 	struct xfs_inode	*ip = XFS_I(file_inode(iocb->ki_filp));
+	unsigned int		dio_flags = 0;
+	const struct iomap_dio_ops *dio_ops = NULL;
 	ssize_t			ret;
 
 	trace_xfs_file_direct_read(iocb, to);
@@ -242,7 +264,12 @@ xfs_file_dio_read(
 	ret = xfs_ilock_iocb(iocb, XFS_IOLOCK_SHARED);
 	if (ret)
 		return ret;
-	ret = iomap_dio_rw(iocb, to, &xfs_read_iomap_ops, NULL, 0, NULL, 0);
+	if (mapping_stable_writes(iocb->ki_filp->f_mapping)) {
+		dio_ops = &xfs_dio_read_bounce_ops;
+		dio_flags |= IOMAP_DIO_BOUNCE;
+	}
+	ret = iomap_dio_rw(iocb, to, &xfs_read_iomap_ops, dio_ops, dio_flags,
+			NULL, 0);
 	xfs_iunlock(ip, XFS_IOLOCK_SHARED);
 
 	return ret;
@@ -703,6 +730,8 @@ xfs_file_dio_write_aligned(
 		xfs_ilock_demote(ip, XFS_IOLOCK_EXCL);
 		iolock = XFS_IOLOCK_SHARED;
 	}
+	if (mapping_stable_writes(iocb->ki_filp->f_mapping))
+		dio_flags |= IOMAP_DIO_BOUNCE;
 	trace_xfs_file_direct_write(iocb, from);
 	ret = iomap_dio_rw(iocb, from, ops, dops, dio_flags, ac, 0);
 out_unlock:
@@ -750,6 +779,7 @@ xfs_file_dio_write_atomic(
 {
 	unsigned int		iolock = XFS_IOLOCK_SHARED;
 	ssize_t			ret, ocount = iov_iter_count(from);
+	unsigned int		dio_flags = 0;
 	const struct iomap_ops	*dops;
 
 	/*
@@ -777,8 +807,10 @@ xfs_file_dio_write_atomic(
 	}
 
 	trace_xfs_file_direct_write(iocb, from);
-	ret = iomap_dio_rw(iocb, from, dops, &xfs_dio_write_ops,
-			0, NULL, 0);
+	if (mapping_stable_writes(iocb->ki_filp->f_mapping))
+		dio_flags |= IOMAP_DIO_BOUNCE;
+	ret = iomap_dio_rw(iocb, from, dops, &xfs_dio_write_ops, dio_flags,
+			NULL, 0);
 
 	/*
 	 * The retry mechanism is based on the ->iomap_begin method returning
@@ -867,6 +899,9 @@ xfs_file_dio_write_unaligned(
 	if (flags & IOMAP_DIO_FORCE_WAIT)
 		inode_dio_wait(VFS_I(ip));
 
+	if (mapping_stable_writes(iocb->ki_filp->f_mapping))
+		flags |= IOMAP_DIO_BOUNCE;
+
 	trace_xfs_file_direct_write(iocb, from);
 	ret = iomap_dio_rw(iocb, from, &xfs_direct_write_iomap_ops,
 			   &xfs_dio_write_ops, flags, NULL, 0);