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[PATCH 02/12] xfsprogs: reserve v5 superblock read-only compat. feature

To: xfs@xxxxxxxxxxx
Subject: [PATCH 02/12] xfsprogs: reserve v5 superblock read-only compat. feature bit for finobt
From: Brian Foster <bfoster@xxxxxxxxxx>
Date: Thu, 10 Oct 2013 11:51:02 -0400
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1381420272-13249-1-git-send-email-bfoster@xxxxxxxxxx>
References: <1381420272-13249-1-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.

Note that this does not yet enable the ability to rw mount a finobt
fs (by setting the feature bit in the XFS_SB_FEAT_RO_COMPAT_ALL

Signed-off-by: Brian Foster <bfoster@xxxxxxxxxx>
 include/xfs_sb.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/include/xfs_sb.h b/include/xfs_sb.h
index c8d8898..83e037b 100644
--- a/include/xfs_sb.h
+++ b/include/xfs_sb.h
@@ -583,6 +583,7 @@ xfs_sb_has_compat_feature(
        return (sbp->sb_features_compat & feature) != 0;
+#define XFS_SB_FEAT_RO_COMPAT_FINOBT   (1 << 0)                /* free inode 
btree */
 static inline bool
@@ -635,6 +636,12 @@ static inline int xfs_sb_version_hasftype(struct xfs_sb 
                xfs_sb_has_incompat_feature(sbp, XFS_SB_FEAT_INCOMPAT_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

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