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[RFC PATCH 02/11] xfs: reserve v5 superblock read-only compat. feature b

To: xfs@xxxxxxxxxxx
Subject: [RFC PATCH 02/11] xfs: reserve v5 superblock read-only compat. feature bit for finobt
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Tue, 3 Sep 2013 14:24:59 -0400
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1378232708-57156-1-git-send-email-bfoster@xxxxxxxxxx>
References: <1378232708-57156-1-git-send-email-bfoster@xxxxxxxxxx>
Reserve a v5 read-only compatibility feature bit for the finobt and
create the xfs_sb_version_hasfinobt() helper to determine whether
an fs has the feature enabled.

The finobt does not change existing on-disk structures, but must
remain consistent with the ialloc btree. Modifications from older
kernels would violate that constrant. Therefore, we restrict older
kernels to read-only mounts of finobt-enabled filesystems.

Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
---
 fs/xfs/xfs_sb.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/xfs_sb.h b/fs/xfs/xfs_sb.h
index 6835b44..c48d95d 100644
--- a/fs/xfs/xfs_sb.h
+++ b/fs/xfs/xfs_sb.h
@@ -585,7 +585,9 @@ xfs_sb_has_compat_feature(
        return (sbp->sb_features_compat & feature) != 0;
 }
 
-#define XFS_SB_FEAT_RO_COMPAT_ALL 0
+#define XFS_SB_FEAT_RO_COMPAT_FINOBT   (1 << 0)                /* free inode 
btree */
+#define XFS_SB_FEAT_RO_COMPAT_ALL \
+               (XFS_SB_FEAT_RO_COMPAT_FINOBT)
 #define XFS_SB_FEAT_RO_COMPAT_UNKNOWN  ~XFS_SB_FEAT_RO_COMPAT_ALL
 static inline bool
 xfs_sb_has_ro_compat_feature(
@@ -639,6 +641,12 @@ static inline int xfs_sb_version_hasftype(struct xfs_sb 
*sbp)
                 (sbp->sb_features2 & XFS_SB_VERSION2_FTYPE));
 }
 
+static inline int xfs_sb_version_hasfinobt(xfs_sb_t *sbp)
+{
+       return (XFS_SB_VERSION_NUM(sbp) == XFS_SB_VERSION_5) &&
+               (sbp->sb_features_ro_compat & XFS_SB_FEAT_RO_COMPAT_FINOBT);
+}
+
 /*
  * end of superblock version macros
  */
-- 
1.8.1.4

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