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Date:	Mon, 10 Nov 2014 11:40:28 -0500
From:	Milosz Tanski <milosz@...in.com>
To:	linux-kernel@...r.kernel.org
Cc:	Christoph Hellwig <hch@....de>,
	Christoph Hellwig <hch@...radead.org>,
	linux-fsdevel@...r.kernel.org, linux-aio@...ck.org,
	Mel Gorman <mgorman@...e.de>,
	Volker Lendecke <Volker.Lendecke@...net.de>,
	Tejun Heo <tj@...nel.org>, Jeff Moyer <jmoyer@...hat.com>,
	Theodore Ts'o <tytso@....edu>,
	Al Viro <viro@...iv.linux.org.uk>, linux-api@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>,
	linux-arch@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: [PATCH v6 5/7] xfs: add RWF_NONBLOCK support

From: Christoph Hellwig <hch@....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@....de>
---
 fs/xfs/xfs_file.c | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index b1f6334..0655915 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -61,6 +61,25 @@ 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;
+		}
+	} else {
+		if (!xfs_ilock_nowait(ip, type))
+			return false;
+	}
+	return true;
+}
+
 static inline void
 xfs_rw_iunlock(
 	struct xfs_inode	*ip,
@@ -246,10 +265,6 @@ 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 +302,14 @@ 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

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