[RFC PATCH v1 06/18] xfs: add iomap async buffered write support

[Stefan Roesch <shr@fb.com>]

This adds the async buffered write support to the iomap layer of XFS. If
a lock cannot be acquired or additional reads need to be performed, the
request will return -EAGAIN in case this is an async buffered write request.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 fs/xfs/xfs_iomap.c | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index e552ce541ec2..80b6c48e88af 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -881,18 +881,28 @@ xfs_buffered_write_iomap_begin(
 	bool			eof = false, cow_eof = false, shared = false;
 	int			allocfork = XFS_DATA_FORK;
 	int			error = 0;
+	bool			no_wait = (flags & IOMAP_NOWAIT);
 
 	if (xfs_is_shutdown(mp))
 		return -EIO;
 
 	/* we can't use delayed allocations when using extent size hints */
-	if (xfs_get_extsz_hint(ip))
+	if (xfs_get_extsz_hint(ip)) {
+		if (no_wait)
+			return -EAGAIN;
+
 		return xfs_direct_write_iomap_begin(inode, offset, count,
 				flags, iomap, srcmap);
+	}
 
 	ASSERT(!XFS_IS_REALTIME_INODE(ip));
 
-	xfs_ilock(ip, XFS_ILOCK_EXCL);
+	if (no_wait) {
+		if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL))
+			return -EAGAIN;
+	} else {
+		xfs_ilock(ip, XFS_ILOCK_EXCL);
+	}
 
 	if (XFS_IS_CORRUPT(mp, !xfs_ifork_has_extents(&ip->i_df)) ||
 	    XFS_TEST_ERROR(false, mp, XFS_ERRTAG_BMAPIFORMAT)) {
@@ -902,6 +912,11 @@ xfs_buffered_write_iomap_begin(
 
 	XFS_STATS_INC(mp, xs_blk_mapw);
 
+	if (no_wait && xfs_need_iread_extents(XFS_IFORK_PTR(ip, XFS_DATA_FORK))) {
+		error = -EAGAIN;
+		goto out_unlock;
+	}
+
 	error = xfs_iread_extents(NULL, ip, XFS_DATA_FORK);
 	if (error)
 		goto out_unlock;
@@ -933,6 +948,10 @@ xfs_buffered_write_iomap_begin(
 	if (xfs_is_cow_inode(ip)) {
 		if (!ip->i_cowfp) {
 			ASSERT(!xfs_is_reflink_inode(ip));
+			if (no_wait) {
+				error = -EAGAIN;
+				goto out_unlock;
+			}
 			xfs_ifork_init_cow(ip);
 		}
 		cow_eof = !xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb,
@@ -956,6 +975,11 @@ xfs_buffered_write_iomap_begin(
 			goto found_imap;
 		}
 
+		if (no_wait) {
+			error = -EAGAIN;
+			goto out_unlock;
+		}
+
 		xfs_trim_extent(&imap, offset_fsb, end_fsb - offset_fsb);
 
 		/* Trim the mapping to the nearest shared extent boundary. */
@@ -993,6 +1017,11 @@ xfs_buffered_write_iomap_begin(
 			allocfork = XFS_COW_FORK;
 	}
 
+	if (no_wait) {
+		error = -EAGAIN;
+		goto out_unlock;
+	}
+
 	error = xfs_qm_dqattach_locked(ip, false);
 	if (error)
 		goto out_unlock;
-- 
2.30.2