[XFS] sort out opening and closing of the block devices

Currently closing the rt/log block device is done in the wrong spot, and
far too early. So revampt it:

- xfs_blkdev_put moved out of xfs_free_buftarg into the caller so that

it is done after tearing down the buftarg completely.

- call to xfs_unmountfs_close moved from xfs_mountfs into caller so

that it's done after tearing down the filesystem completely.

- xfs_unmountfs_close is renamed to xfs_close_devices and made static

in xfs_super.c

- opening of the block devices is split into a helper xfs_open_devices

that is symetric in use to xfs_close_devices

- xfs_unmountfs can now lose struct cred

- error handling around device opening sanitized in xfs_fs_fill_super

SGI-PV: 981951
SGI-Modid: xfs-linux-melb:xfs-kern:31193a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 4aff0c1..5acde7f 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -518,8 +518,7 @@
 extern int	xfs_mountfs(xfs_mount_t *mp, int);
 extern void	xfs_mountfs_check_barriers(xfs_mount_t *mp);
 
-extern int	xfs_unmountfs(xfs_mount_t *, struct cred *);
-extern void	xfs_unmountfs_close(xfs_mount_t *, struct cred *);
+extern int	xfs_unmountfs(xfs_mount_t *);
 extern int	xfs_unmountfs_writesb(xfs_mount_t *);
 extern int	xfs_unmount_flush(xfs_mount_t *, int);
 extern int	xfs_mod_incore_sb(xfs_mount_t *, xfs_sb_field_t, int64_t, int);