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[PATCH 1/3 v2] xfs: add RWF_NONBLOCK support

To: Milosz Tanski <milosz@xxxxxxxxx>
Subject: [PATCH 1/3 v2] xfs: add RWF_NONBLOCK support
From: Christoph Hellwig <hch@xxxxxx>
Date: Thu, 2 Oct 2014 19:33:47 +0200
Cc: linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, Dave Chinner <david@xxxxxxxxxxxxx>
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1412197494-7655-2-git-send-email-hch@xxxxxx>
References: <1412197494-7655-1-git-send-email-hch@xxxxxx> <1412197494-7655-2-git-send-email-hch@xxxxxx>
User-agent: Mutt/1.5.17 (2007-11-01)
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@xxxxxx>
---
 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 cf61271..6981b10 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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