[XFS] Ensure "both" features2 slots are consistent
Since older kernels may look in the sb_bad_features2 slot for flags,
rather than zeroing it out on fixup, we should make it equal to the
sb_features2 value.
Also, if the ATTR2 flag was not found prior to features2 fixup, it was not
set in the mount flags, so re-check after the fixup so that the current
session will use the feature.
Also fix up the comments to reflect these changes.
SGI-PV: 980085
SGI-Modid: xfs-linux-melb:xfs-kern:30778a
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 4e93c02..8ed164e 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -972,23 +972,35 @@
xfs_mount_common(mp, sbp);
/*
- * Check for a bad features2 field alignment. This happened on
- * some platforms due to xfs_sb_t not being 64bit size aligned
- * when sb_features was added and hence the compiler put it in
- * the wrong place.
+ * Check for a mismatched features2 values. Older kernels
+ * read & wrote into the wrong sb offset for sb_features2
+ * on some platforms due to xfs_sb_t not being 64bit size aligned
+ * when sb_features2 was added, which made older superblock
+ * reading/writing routines swap it as a 64-bit value.
*
- * If we detect a bad field, we or the set bits into the existing
- * features2 field in case it has already been modified and we
- * don't want to lose any features. Zero the bad one and mark
- * the two fields as needing updates once the transaction subsystem
- * is online.
+ * For backwards compatibility, we make both slots equal.
+ *
+ * If we detect a mismatched field, we OR the set bits into the
+ * existing features2 field in case it has already been modified; we
+ * don't want to lose any features. We then update the bad location
+ * with the ORed value so that older kernels will see any features2
+ * flags, and mark the two fields as needing updates once the
+ * transaction subsystem is online.
*/
- if (xfs_sb_has_bad_features2(sbp)) {
+ if (xfs_sb_has_mismatched_features2(sbp)) {
cmn_err(CE_WARN,
"XFS: correcting sb_features alignment problem");
sbp->sb_features2 |= sbp->sb_bad_features2;
- sbp->sb_bad_features2 = 0;
+ sbp->sb_bad_features2 = sbp->sb_features2;
update_flags |= XFS_SB_FEATURES2 | XFS_SB_BAD_FEATURES2;
+
+ /*
+ * Re-check for ATTR2 in case it was found in bad_features2
+ * slot.
+ */
+ if (xfs_sb_version_hasattr2(&mp->m_sb))
+ mp->m_flags |= XFS_MOUNT_ATTR2;
+
}
/*
@@ -1896,7 +1908,8 @@
/*
* Used to log changes to the superblock unit and width fields which could
- * be altered by the mount options. Only the first superblock is updated.
+ * be altered by the mount options, as well as any potential sb_features2
+ * fixup. Only the first superblock is updated.
*/
STATIC void
xfs_mount_log_sb(