[PATCH 1/3] xfs: add RWF_NONBLOCK support

[Christoph Hellwig <hch@lst.de>]

Add support for non-blocking reads.  The guts are handled by the generic
code, the only addition is a non-blocking variant of xfs_rw_ilock.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/xfs/xfs_file.c | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index cf61271..f9efffc 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -61,6 +61,23 @@ xfs_rw_ilock(
 	xfs_ilock(ip, type);
 }
 
+static inline bool
+xfs_rw_ilock_nowait(
+	struct xfs_inode	*ip,
+	int			type)
+{
+	if (type & XFS_IOLOCK_EXCL) {
+		if (!mutex_trylock(&VFS_I(ip)->i_mutex))
+			return false;
+	}
+	if (!xfs_ilock_nowait(ip, type)) {
+		mutex_unlock(&VFS_I(ip)->i_mutex);
+		return false;
+	}
+
+	return true;
+}
+
 static inline void
 xfs_rw_iunlock(
 	struct xfs_inode	*ip,
@@ -246,10 +263,6 @@ xfs_file_read_iter(
 
 	XFS_STATS_INC(xs_read_calls);
 
-	/* XXX: need a non-blocking iolock helper, shouldn't be too hard */
-	if (iocb->ki_rwflags & RWF_NONBLOCK)
-		return -EAGAIN;
-
 	if (unlikely(file->f_flags & O_DIRECT))
 		ioflags |= XFS_IO_ISDIRECT;
 	if (file->f_mode & FMODE_NOCMTIME)
@@ -287,7 +300,14 @@ xfs_file_read_iter(
 	 * This allows the normal direct IO case of no page cache pages to
 	 * proceeed concurrently without serialisation.
 	 */
-	xfs_rw_ilock(ip, XFS_IOLOCK_SHARED);
+	if (iocb->ki_rwflags & RWF_NONBLOCK) {
+		if (ioflags & XFS_IO_ISDIRECT)
+			return -EAGAIN;
+		if (!xfs_rw_ilock_nowait(ip, XFS_IOLOCK_SHARED))
+			return -EAGAIN;
+	} else {
+		xfs_rw_ilock(ip, XFS_IOLOCK_SHARED);
+	}
 	if ((ioflags & XFS_IO_ISDIRECT) && inode->i_mapping->nrpages) {
 		xfs_rw_iunlock(ip, XFS_IOLOCK_SHARED);
 		xfs_rw_ilock(ip, XFS_IOLOCK_EXCL);
-- 
1.9.1