[PATCH 3/3] xfs: fallback to buffered I/O if direct I/O is short

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

From: Goldwyn Rodrigues <rgoldwyn@suse.com>

Most filesystems such as ext4 and btrfs fallback to buffered I/O in case
direct write's fail. In case direct I/O is short, fallback to buffered
write to complete the I/O. Make sure the data is on disk by performing a
filemap_write_and_wait_range() and invalidating the pages in the range.

For reads, call xfs_file_buffered_aio_read() in case of short I/O.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/xfs/xfs_file.c | 41 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 4b8bdecc3863..786391228dea 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -31,6 +31,10 @@
 #include <linux/fadvise.h>
 
 static const struct vm_operations_struct xfs_file_vm_ops;
+STATIC ssize_t xfs_file_buffered_aio_write(struct kiocb *iocb,
+		struct iov_iter	*from);
+STATIC ssize_t xfs_file_buffered_aio_read(struct kiocb *iocb,
+		struct iov_iter	*to);
 
 int
 xfs_update_prealloc_flags(
@@ -169,6 +173,7 @@ xfs_file_dio_aio_read(
 	struct xfs_inode	*ip = XFS_I(file_inode(iocb->ki_filp));
 	size_t			count = iov_iter_count(to);
 	ssize_t			ret;
+	ssize_t			buffered_read = 0;
 
 	trace_xfs_file_direct_read(ip, count, iocb->ki_pos);
 
@@ -187,7 +192,13 @@ xfs_file_dio_aio_read(
 			is_sync_kiocb(iocb));
 	xfs_iunlock(ip, XFS_IOLOCK_SHARED);
 
-	return ret;
+	if (ret < 0 || ret == count)
+		return ret;
+
+	iocb->ki_flags &= ~IOCB_DIRECT;
+	buffered_read = xfs_file_buffered_aio_read(iocb, to);
+
+	return ret + buffered_read;
 }
 
 static noinline ssize_t
@@ -483,6 +494,9 @@ xfs_file_dio_aio_write(
 	int			iolock;
 	size_t			count = iov_iter_count(from);
 	struct xfs_buftarg      *target = xfs_inode_buftarg(ip);
+	loff_t			offset, end;
+	ssize_t			buffered_write = 0;
+	int			err;
 
 	/* DIO must be aligned to device logical sector size */
 	if ((iocb->ki_pos | count) & target->bt_logical_sectormask)
@@ -552,12 +566,25 @@ xfs_file_dio_aio_write(
 out:
 	xfs_iunlock(ip, iolock);
 
-	/*
-	 * No fallback to buffered IO on errors for XFS, direct IO will either
-	 * complete fully or fail.
-	 */
-	ASSERT(ret < 0 || ret == count);
-	return ret;
+	if (ret < 0 || ret == count)
+		return ret;
+
+	/* Fallback to buffered write */
+
+	offset = iocb->ki_pos;
+
+	buffered_write = xfs_file_buffered_aio_write(iocb, from);
+	if (buffered_write < 0)
+		return ret;
+
+	end = offset + buffered_write - 1;
+
+	err = filemap_write_and_wait_range(mapping, offset, end);
+	if (!err)
+		invalidate_mapping_pages(mapping, offset >> PAGE_SHIFT,
+				end >> PAGE_SHIFT);
+
+	return ret + buffered_write;
 }
 
 static noinline ssize_t
-- 
2.25.0