[PATCH 4/5] xfs: make sure xfs_sync_fsdata covers the log

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

We want to always cover the log after writing out the superblock, and
in case of a synchronous writeout make sure we actually wait for the
log to be covered.  That way a filesystem that has been sync()ed can
be considered clean by log recovery.

Index: linux-2.6/fs/xfs/linux-2.6/xfs_sync.c
===================================================================
--- linux-2.6.orig/fs/xfs/linux-2.6/xfs_sync.c  2009-04-26 10:08:01.468074092 
+0200
+++ linux-2.6/fs/xfs/linux-2.6/xfs_sync.c       2009-04-26 10:28:37.049956907 
+0200
@@ -208,11 +210,15 @@ xfs_sync_inodes(
 STATIC int
 xfs_commit_dummy_trans(
        struct xfs_mount        *mp,
-       uint                    log_flags)
+       uint                    flags)
 {
        struct xfs_inode        *ip = mp->m_rootip;
        struct xfs_trans        *tp;
        int                     error;
+       int                     log_flags = XFS_LOG_FORCE;
+
+       if (flags & SYNC_WAIT)
+               log_flags |= XFS_LOG_SYNC;
 
        /*
         * Put a dummy transaction in the log to tell recovery
@@ -230,13 +236,12 @@ xfs_commit_dummy_trans(
        xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
        xfs_trans_ihold(tp, ip);
        xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
-       /* XXX(hch): ignoring the error here.. */
        error = xfs_trans_commit(tp, 0);
-
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
 
+       /* the log force ensures this transaction is pushed to disk */
        xfs_log_force(mp, 0, log_flags);
-       return 0;
+       return error;
 }
 
 int
@@ -276,6 +281,7 @@ xfs_sync_fsdata(
                 */
                if (XFS_BUF_ISPINNED(bp))
                        xfs_log_force(mp, 0, XFS_LOG_FORCE);
+               xfs_flush_buftarg(mp->m_ddev_targp, 1);
        }
 
 
@@ -284,7 +290,10 @@ xfs_sync_fsdata(
        else
                XFS_BUF_ASYNC(bp);
 
-       return xfs_bwrite(mp, bp);
+       error = xfs_bwrite(mp, bp);
+       if (!error && xfs_log_need_covered(mp))
+               error = xfs_commit_dummy_trans(mp, (flags & SYNC_WAIT));
+       return error;
 
  out_brelse:
        xfs_buf_relse(bp);
@@ -469,8 +478,6 @@ xfs_sync_worker(
                /* dgc: errors ignored here */
                error = XFS_QM_DQSYNC(mp, SYNC_BDFLUSH);
                error = xfs_sync_fsdata(mp, SYNC_BDFLUSH);
-               if (xfs_log_need_covered(mp))
-                       error = xfs_commit_dummy_trans(mp, XFS_LOG_FORCE);
        }
        mp->m_sync_seq++;
        wake_up(&mp->m_wait_single_sync_task);