xfs: check the realtime superblock at mount time

Check the realtime superblock at mount time, to ensure that the label
and uuids actually match the primary superblock on the data device.  If
the rt superblock is good, attach it to the xfs_mount so that the log
can use ordered buffers to keep this primary in sync with the primary
super on the data device.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_mount.h

@@ -119,6 +119,7 @@ typedef struct xfs_mount {
 	struct super_block	*m_super;
 	struct xfs_ail		*m_ail;		/* fs active log item list */
 	struct xfs_buf		*m_sb_bp;	/* buffer for superblock */
+	struct xfs_buf		*m_rtsb_bp;	/* realtime superblock */
 	char			*m_rtname;	/* realtime device name */
 	char			*m_logname;	/* external log device name */
 	struct xfs_da_geometry	*m_dir_geo;	/* directory block geometry */

fs/xfs/xfs_rtalloc.c

@@ -1152,6 +1152,56 @@ xfs_growfs_rt(
 	return error;
 }
 
+/* Read the realtime superblock and attach it to the mount. */
+int
+xfs_rtmount_readsb(
+	struct xfs_mount	*mp)
+{
+	struct xfs_buf		*bp;
+	int			error;
+
+	if (!xfs_has_rtsb(mp))
+		return 0;
+	if (mp->m_sb.sb_rblocks == 0)
+		return 0;
+	if (mp->m_rtdev_targp == NULL) {
+		xfs_warn(mp,
+	"Filesystem has a realtime volume, use rtdev=device option");
+		return -ENODEV;
+	}
+
+	/* m_blkbb_log is not set up yet */
+	error = xfs_buf_read_uncached(mp->m_rtdev_targp, XFS_RTSB_DADDR,
+			mp->m_sb.sb_blocksize >> BBSHIFT, XBF_NO_IOACCT, &bp,
+			&xfs_rtsb_buf_ops);
+	if (error) {
+		xfs_warn(mp, "rt sb validate failed with error %d.", error);
+		/* bad CRC means corrupted metadata */
+		if (error == -EFSBADCRC)
+			error = -EFSCORRUPTED;
+		return error;
+	}
+
+	mp->m_rtsb_bp = bp;
+	xfs_buf_unlock(bp);
+	return 0;
+}
+
+/* Detach the realtime superblock from the mount and free it. */
+void
+xfs_rtmount_freesb(
+	struct xfs_mount	*mp)
+{
+	struct xfs_buf		*bp = mp->m_rtsb_bp;
+
+	if (!bp)
+		return;
+
+	xfs_buf_lock(bp);
+	mp->m_rtsb_bp = NULL;
+	xfs_buf_relse(bp);
+}
+
 /*
  * Initialize realtime fields in the mount structure.
  */

fs/xfs/xfs_rtalloc.h

@@ -12,6 +12,10 @@ struct xfs_mount;
 struct xfs_trans;
 
 #ifdef CONFIG_XFS_RT
+/* rtgroup superblock initialization */
+int xfs_rtmount_readsb(struct xfs_mount *mp);
+void xfs_rtmount_freesb(struct xfs_mount *mp);
+
 /*
  * Initialize realtime fields in the mount structure.
  */
@@ -42,6 +46,8 @@ int xfs_rtalloc_reinit_frextents(struct xfs_mount *mp);
 #else
 # define xfs_growfs_rt(mp,in)				(-ENOSYS)
 # define xfs_rtalloc_reinit_frextents(m)		(0)
+# define xfs_rtmount_readsb(mp)				(0)
+# define xfs_rtmount_freesb(mp)				((void)0)
 static inline int		/* error */
 xfs_rtmount_init(
 	xfs_mount_t	*mp)	/* file system mount structure */

fs/xfs/xfs_super.c

@@ -45,6 +45,7 @@
 #include "xfs_rtbitmap.h"
 #include "xfs_exchmaps_item.h"
 #include "xfs_parent.h"
+#include "xfs_rtalloc.h"
 #include "scrub/stats.h"
 #include "scrub/rcbag_btree.h"
 
@@ -1145,6 +1146,7 @@ xfs_fs_put_super(
 	xfs_filestream_unmount(mp);
 	xfs_unmountfs(mp);
 
+	xfs_rtmount_freesb(mp);
 	xfs_freesb(mp);
 	xchk_mount_stats_free(mp);
 	free_percpu(mp->m_stats.xs_stats);
@@ -1690,10 +1692,14 @@ xfs_fs_fill_super(
 		goto out_free_sb;
 	}
 
-	error = xfs_filestream_mount(mp);
+	error = xfs_rtmount_readsb(mp);
 	if (error)
 		goto out_free_sb;
 
+	error = xfs_filestream_mount(mp);
+	if (error)
+		goto out_free_rtsb;
+
 	/*
 	 * we must configure the block size in the superblock before we run the
 	 * full mount process as the mount process can lookup and cache inodes.
@@ -1781,6 +1787,8 @@ xfs_fs_fill_super(
 
  out_filestream_unmount:
 	xfs_filestream_unmount(mp);
+ out_free_rtsb:
+	xfs_rtmount_freesb(mp);
  out_free_sb:
 	xfs_freesb(mp);
  out_free_scrub_stats:
@@ -1800,7 +1808,7 @@ xfs_fs_fill_super(
  out_unmount:
 	xfs_filestream_unmount(mp);
 	xfs_unmountfs(mp);
-	goto out_free_sb;
+	goto out_free_rtsb;
 }
 
 static int