xfs: only issues a cache flush on unmount if barriers are enabled

Currently we unconditionally issue a flush from xfs_free_buftarg, but
since 2.6.29-rc1 this gives a warning in the style of

	end_request: I/O error, dev vdb, sector 0

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

fs/xfs/linux-2.6/xfs_buf.c

@@ -34,6 +34,12 @@
 #include <linux/backing-dev.h>
 #include <linux/freezer.h>
 
+#include "xfs_sb.h"
+#include "xfs_inum.h"
+#include "xfs_ag.h"
+#include "xfs_dmapi.h"
+#include "xfs_mount.h"
+
 static kmem_zone_t *xfs_buf_zone;
 STATIC int xfsbufd(void *);
 STATIC int xfsbufd_wakeup(int, gfp_t);
@@ -1435,10 +1441,12 @@ xfs_unregister_buftarg(
 
 void
 xfs_free_buftarg(
-	xfs_buftarg_t		*btp)
+	struct xfs_mount	*mp,
+	struct xfs_buftarg	*btp)
 {
 	xfs_flush_buftarg(btp, 1);
-	xfs_blkdev_issue_flush(btp);
+	if (mp->m_flags & XFS_MOUNT_BARRIER)
+		xfs_blkdev_issue_flush(btp);
 	xfs_free_bufhash(btp);
 	iput(btp->bt_mapping->host);
 

fs/xfs/linux-2.6/xfs_buf.h

@@ -413,7 +413,7 @@ static inline int XFS_bwrite(xfs_buf_t *bp)
  *	Handling of buftargs.
  */
 extern xfs_buftarg_t *xfs_alloc_buftarg(struct block_device *, int);
-extern void xfs_free_buftarg(xfs_buftarg_t *);
+extern void xfs_free_buftarg(struct xfs_mount *, struct xfs_buftarg *);
 extern void xfs_wait_buftarg(xfs_buftarg_t *);
 extern int xfs_setsize_buftarg(xfs_buftarg_t *, unsigned int, unsigned int);
 extern int xfs_flush_buftarg(xfs_buftarg_t *, int);

fs/xfs/linux-2.6/xfs_super.c

@@ -733,15 +733,15 @@ xfs_close_devices(
 {
 	if (mp->m_logdev_targp && mp->m_logdev_targp != mp->m_ddev_targp) {
 		struct block_device *logdev = mp->m_logdev_targp->bt_bdev;
-		xfs_free_buftarg(mp->m_logdev_targp);
+		xfs_free_buftarg(mp, mp->m_logdev_targp);
 		xfs_blkdev_put(logdev);
 	}
 	if (mp->m_rtdev_targp) {
 		struct block_device *rtdev = mp->m_rtdev_targp->bt_bdev;
-		xfs_free_buftarg(mp->m_rtdev_targp);
+		xfs_free_buftarg(mp, mp->m_rtdev_targp);
 		xfs_blkdev_put(rtdev);
 	}
-	xfs_free_buftarg(mp->m_ddev_targp);
+	xfs_free_buftarg(mp, mp->m_ddev_targp);
 }
 
 /*
@@ -810,9 +810,9 @@ xfs_open_devices(
 
  out_free_rtdev_targ:
 	if (mp->m_rtdev_targp)
-		xfs_free_buftarg(mp->m_rtdev_targp);
+		xfs_free_buftarg(mp, mp->m_rtdev_targp);
  out_free_ddev_targ:
-	xfs_free_buftarg(mp->m_ddev_targp);
+	xfs_free_buftarg(mp, mp->m_ddev_targp);
  out_close_rtdev:
 	if (rtdev)
 		xfs_blkdev_put(rtdev);