[PATCH 2/4] xfs: New function for secondary superblock updates

[Eric Sandeen <sandeen@redhat.com>]

Relabel must update all secondary superblocks, as offline relabel does.

This is essentially a simpler copy of the current growfs code, which is
undergoing an independent refactor; we can see about merging stuff back
together after all this work is done.  In the meantime, this is a fairly
small, simple bit of code to facilitate the online label work.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---
 fs/xfs/xfs_fsops.c | 48 ++++++++++++++++++++++++++++++++++++++++++++++
 fs/xfs/xfs_fsops.h |  1 +
 2 files changed, 49 insertions(+)

diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
index 523792768080..1aaa93051f78 100644
--- a/fs/xfs/xfs_fsops.c
+++ b/fs/xfs/xfs_fsops.c
@@ -71,6 +71,54 @@ xfs_growfs_get_hdr_buf(
 	return bp;
 }
 
+/*
+ * Copy the contents of the primary super to all backup supers.
+ * Not currently used for growfs, as it only looks at existing supers.
+ */
+int
+xfs_update_secondary_supers(
+	xfs_mount_t		*mp)
+{
+	int			error, saved_error;
+	xfs_agnumber_t		agno;
+	xfs_buf_t		*bp;
+
+	error = saved_error = 0;
+
+	for (agno = 1; agno < mp->m_sb.sb_agcount; agno++) {
+		error = xfs_trans_read_buf(mp, NULL, mp->m_ddev_targp,
+			  XFS_AGB_TO_DADDR(mp, agno, XFS_SB_BLOCK(mp)),
+			  XFS_FSS_TO_BB(mp, 1), 0, &bp, &xfs_sb_buf_ops);
+		/*
+		 * If we get an error reading or writing alternate superblocks,
+		 * continue.  xfs_repair chooses the "best" superblock based
+		 * on most matches; if we break early, we'll leave more
+		 * superblocks un-updated than updated, and xfs_repair may
+		 * pick them over the properly-updated primary.
+		 */
+		if (error) {
+			xfs_warn(mp,
+		"error %d reading secondary superblock for ag %d",
+				error, agno);
+			saved_error = error;
+			continue;
+		}
+		xfs_sb_to_disk(XFS_BUF_TO_SBP(bp), &mp->m_sb);
+
+		error = xfs_bwrite(bp);
+		xfs_buf_relse(bp);
+		if (error) {
+			xfs_warn(mp,
+		"write error %d updating secondary superblock for ag %d",
+				error, agno);
+			saved_error = error;
+			continue;
+		}
+	}
+
+	return saved_error ? saved_error : error;
+}
+
 static int
 xfs_growfs_data_private(
 	xfs_mount_t		*mp,		/* mount point for filesystem */
diff --git a/fs/xfs/xfs_fsops.h b/fs/xfs/xfs_fsops.h
index 20484ed5e919..257d3018bc39 100644
--- a/fs/xfs/xfs_fsops.h
+++ b/fs/xfs/xfs_fsops.h
@@ -18,6 +18,7 @@
 #ifndef __XFS_FSOPS_H__
 #define	__XFS_FSOPS_H__
 
+extern int xfs_update_secondary_supers(xfs_mount_t *mp);
 extern int xfs_growfs_data(xfs_mount_t *mp, xfs_growfs_data_t *in);
 extern int xfs_growfs_log(xfs_mount_t *mp, xfs_growfs_log_t *in);
 extern int xfs_fs_counts(xfs_mount_t *mp, xfs_fsop_counts_t *cnt);
-- 
2.17.0