[XFS] write barrier support Issue all log sync operations as ordered

writes.  In addition flush the disk cache on fsync if the sync cached
operation didn't sync the log to disk (this requires some additional
bookeping in the transaction and log code). If the device doesn't claim to
support barriers, the filesystem has an extern log volume or the trial
superblock write with barriers enabled failed we disable barriers and
print a warning.  We should probably fail the mount completely, but that
could lead to nasty boot failures for the root filesystem.  Not enabled by
default yet, needs more destructive testing first.

SGI-PV: 912426
SGI-Modid: xfs-linux:xfs-kern:198723a

Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/fs/xfs/linux-2.6/xfs_super.c b/fs/xfs/linux-2.6/xfs_super.c
index 2302454d8d4..d2701cc624b 100644
--- a/fs/xfs/linux-2.6/xfs_super.c
+++ b/fs/xfs/linux-2.6/xfs_super.c
@@ -278,6 +278,72 @@ xfs_blkdev_put(
                 close_bdev_excl(bdev);
 }
 
+/*
+ * Try to write out the superblock using barriers.
+ */
+STATIC int
+xfs_barrier_test(
+        xfs_mount_t     *mp)
+{
+        xfs_buf_t       *sbp = xfs_getsb(mp, 0);
+        int             error;
+
+        XFS_BUF_UNDONE(sbp);
+        XFS_BUF_UNREAD(sbp);
+        XFS_BUF_UNDELAYWRITE(sbp);
+        XFS_BUF_WRITE(sbp);
+        XFS_BUF_UNASYNC(sbp);
+        XFS_BUF_ORDERED(sbp);
+
+        xfsbdstrat(mp, sbp);
+        error = xfs_iowait(sbp);
+
+        /*
+         * Clear all the flags we set and possible error state in the
+         * buffer.  We only did the write to try out whether barriers
+         * worked and shouldn't leave any traces in the superblock
+         * buffer.
+         */
+        XFS_BUF_DONE(sbp);
+        XFS_BUF_ERROR(sbp, 0);
+        XFS_BUF_UNORDERED(sbp);
+
+        xfs_buf_relse(sbp);
+        return error;
+}
+
+void
+xfs_mountfs_check_barriers(xfs_mount_t *mp)
+{
+        int error;
+
+        if (mp->m_logdev_targp != mp->m_ddev_targp) {
+                xfs_fs_cmn_err(CE_NOTE, mp,
+                  "Disabling barriers, not supported with external log device");
+                mp->m_flags &= ~XFS_MOUNT_BARRIER;
+        }
+
+        if (mp->m_ddev_targp->pbr_bdev->bd_disk->queue->ordered ==
+                                        QUEUE_ORDERED_NONE) {
+                xfs_fs_cmn_err(CE_NOTE, mp,
+                  "Disabling barriers, not supported by the underlying device");
+                mp->m_flags &= ~XFS_MOUNT_BARRIER;
+        }
+
+        error = xfs_barrier_test(mp);
+        if (error) {
+                xfs_fs_cmn_err(CE_NOTE, mp,
+                  "Disabling barriers, trial barrier write failed");
+                mp->m_flags &= ~XFS_MOUNT_BARRIER;
+        }
+}
+
+void
+xfs_blkdev_issue_flush(
+        xfs_buftarg_t           *buftarg)
+{
+        blkdev_issue_flush(buftarg->pbr_bdev, NULL);
+}
 
 STATIC struct inode *
 linvfs_alloc_inode(