On Sun, Mar 30, 2008 at 10:03:08PM -0500, Eric Sandeen wrote:
> 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
> @@ -967,22 +967,26 @@ 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;
Probably should update XFS_MOUNT_ATTR2 here, not later. i.e. before
we mount he log and start recovery.
> @@ -1181,6 +1185,12 @@ xfs_mountfs(
> xfs_mount_log_sb(mp, update_flags);
>
> /*
> + * 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;
> +
Rather than here.
> /*
> - * 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);
> }
Yep, makes sense.
Cheers,
Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group
|