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[PATCH V2] combined features2 fixup patches (updating/rewriting what was

To: David Chinner <dgc@xxxxxxx>
Subject: [PATCH V2] combined features2 fixup patches (updating/rewriting what was sent in other threads)
From: Eric Sandeen <sandeen@xxxxxxxxxxx>
Date: Wed, 02 Apr 2008 20:06:21 -0500
Cc: xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <20080402002940.GZ103491721@xxxxxxx>
References: <47F0546C.9070709@xxxxxxxxxxx> <20080402002940.GZ103491721@xxxxxxx>
Sender: xfs-bounce@xxxxxxxxxxx
User-agent: Thunderbird 2.0.0.12 (Macintosh/20080213)
(Addressing Dave's review point)

Ensure "both" features2 slots are consistent, and set mp attr2 flag.

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.

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxxx>
---

Index: linux-2.6-xfs/fs/xfs/xfs_mount.c
===================================================================
--- linux-2.6-xfs.orig/fs/xfs/xfs_mount.c
+++ linux-2.6-xfs/fs/xfs/xfs_mount.c
@@ -967,23 +967,32 @@ xfs_mountfs(
        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 from the bad_features2 slot.
+                */
+               if (xfs_sb_version_hasattr2(&mp->m_sb))
+                       mp->m_flags |= XFS_MOUNT_ATTR2;
        }
 
        /*
@@ -1890,7 +1899,8 @@ xfs_uuid_unmount(
 
 /*
  * 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(
Index: linux-2.6-xfs/fs/xfs/xfs_sb.h
===================================================================
--- linux-2.6-xfs.orig/fs/xfs/xfs_sb.h
+++ linux-2.6-xfs/fs/xfs/xfs_sb.h
@@ -320,11 +320,12 @@ static inline int xfs_sb_good_version(xf
 #endif /* __KERNEL__ */
 
 /*
- * Detect a bad features2 field
+ * Detect a mismatched features2 field.  Older kernels read/wrote
+ * this into the wrong slot, so to be safe we keep them in sync.
  */
-static inline int xfs_sb_has_bad_features2(xfs_sb_t *sbp)
+static inline int xfs_sb_has_mismatched_features2(xfs_sb_t *sbp)
 {
-       return (sbp->sb_bad_features2 != 0);
+       return (sbp->sb_bad_features2 != sbp->sb_features2);
 }
 
 static inline unsigned xfs_sb_version_tonew(unsigned v)



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