[PATCH v5 06/10] xfs: Add xfs_file_dio_write_atomic()

[John Garry]

Add xfs_file_dio_write_atomic() for dedicated handling of atomic writes.

In case of -EAGAIN being returned from iomap_dio_rw(), reissue the write
in CoW-based atomic write mode.

For CoW-based mode, ensure that we have no outstanding IOs which we
may trample on.

Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>
Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
---
 fs/xfs/xfs_file.c | 44 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 75a6d7e75bf8..ddcf95ce741e 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -725,6 +725,46 @@ xfs_file_dio_write_zoned(
 	return ret;
 }
 
+static noinline ssize_t
+xfs_file_dio_write_atomic(
+	struct xfs_inode	*ip,
+	struct kiocb		*iocb,
+	struct iov_iter		*from)
+{
+	unsigned int		iolock = XFS_IOLOCK_SHARED;
+	unsigned int		dio_flags = 0;
+	ssize_t			ret;
+
+retry:
+	ret = xfs_ilock_iocb_for_write(iocb, &iolock);
+	if (ret)
+		return ret;
+
+	ret = xfs_file_write_checks(iocb, from, &iolock, NULL);
+	if (ret)
+		goto out_unlock;
+
+	if (dio_flags & IOMAP_DIO_FORCE_WAIT)
+		inode_dio_wait(VFS_I(ip));
+
+	trace_xfs_file_direct_write(iocb, from);
+	ret = iomap_dio_rw(iocb, from, &xfs_atomic_write_iomap_ops,
+			&xfs_dio_write_ops, dio_flags, NULL, 0);
+
+	if (ret == -EAGAIN && !(iocb->ki_flags & IOCB_NOWAIT) &&
+	    !(dio_flags & IOMAP_DIO_ATOMIC_SW)) {
+		xfs_iunlock(ip, iolock);
+		dio_flags = IOMAP_DIO_ATOMIC_SW | IOMAP_DIO_FORCE_WAIT;
+		iolock = XFS_IOLOCK_EXCL;
+		goto retry;
+	}
+
+out_unlock:
+	if (iolock)
+		xfs_iunlock(ip, iolock);
+	return ret;
+}
+
 /*
  * Handle block unaligned direct I/O writes
  *
@@ -840,6 +880,10 @@ xfs_file_dio_write(
 		return xfs_file_dio_write_unaligned(ip, iocb, from);
 	if (xfs_is_zoned_inode(ip))
 		return xfs_file_dio_write_zoned(ip, iocb, from);
+
+	if (iocb->ki_flags & IOCB_ATOMIC)
+		return xfs_file_dio_write_atomic(ip, iocb, from);
+
 	return xfs_file_dio_write_aligned(ip, iocb, from,
 			&xfs_direct_write_iomap_ops, &xfs_dio_write_ops, NULL);
 }
-- 
2.31.1