xfs: merge fsync and O_SYNC handling

The guarantees for O_SYNC are exactly the same as the ones we need to
make for an fsync call (and given that Linux O_SYNC is O_DSYNC the
equivalent is fdadatasync, but we treat both the same in XFS), except
with a range data writeout.  Jan Kara has started unifying these two
path for filesystems using the generic helpers, and I've started to
look at XFS.

The actual transaction commited by xfs_fsync and xfs_write_sync_logforce
has a different transaction number, but actually is exactly the same.
We'll only use the fsync transaction going forward.  One major difference
is that xfs_write_sync_logforce never issues a cache flush unless we
commit a transaction causing that as a side-effect, which is an obvious
bug in the O_SYNC handling.  Second all the locking and i_update_size
vs i_update_core changes from 978b7237123d007b9fa983af6e0e2fa8f97f9934
never made it to xfs_write_sync_logforce, so we add them back.

To make xfs_fsync easily usable from the O_SYNC path, the filemap_fdatawait
call is moved up to xfs_file_fsync, so that we don't wait on the whole
file after we already waited for our portion in xfs_write.

We'll also use a plain call to filemap_write_and_wait_range instead
of the previous sync_page_rang which did it in two steps including
an half-hearted inode write out that doesn't help us.

Once we're done with this also remove the now useless i_update_size
tracking.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Felix Blyakher <felixb@sgi.com>
Signed-off-by: Felix Blyakher <felixb@sgi.com>

1 files changed, 14 insertions, 5 deletions

diff --git a/fs/xfs/linux-2.6/xfs_file.c b/fs/xfs/linux-2.6/xfs_file.c
index 0542fd507649..988d8f87bc0f 100644
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -172,12 +172,21 @@ xfs_file_release(
  */
 STATIC int
 xfs_file_fsync(
-        struct file     *filp,
-        struct dentry   *dentry,
-        int             datasync)
+        struct file             *file,
+        struct dentry           *dentry,
+        int                     datasync)
 {
-        xfs_iflags_clear(XFS_I(dentry->d_inode), XFS_ITRUNCATED);
-        return -xfs_fsync(XFS_I(dentry->d_inode));
+        struct inode            *inode = dentry->d_inode;
+        struct xfs_inode        *ip = XFS_I(inode);
+        int                     error;
+
+        /* capture size updates in I/O completion before writing the inode. */
+        error = filemap_fdatawait(inode->i_mapping);
+        if (error)
+                return error;
+
+        xfs_iflags_clear(ip, XFS_ITRUNCATED);
+        return -xfs_fsync(ip);
 }
 
 STATIC int