[PATCH 10/18] xfs: set sparse inodes feature bit when a sparse chunk is allocated

[Brian Foster <bfoster@redhat.com>]

The sparse chunk inode record format is backwards compatible with old
format inobt records as long as full chunks are allocated. The holemask
field uses higher order bytes of the freecount. While sparse chunks can
be enabled on previously unsupported fs, older kernel drivers cannot
parse sparse inode records.

Set the feature incompatible bit once a sparse inode chunk is allocated
to prevent older XFS drivers from tripping over the new format.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---
 fs/xfs/libxfs/xfs_ialloc.c | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
index 4226b1b..4dd45c2 100644
--- a/fs/xfs/libxfs/xfs_ialloc.c
+++ b/fs/xfs/libxfs/xfs_ialloc.c
@@ -407,6 +407,27 @@ error:
 	return error;
 }
 
+STATIC void
+xfs_sbversion_add_spinodes(
+	struct xfs_trans	*tp,
+	struct xfs_mount	*mp)
+{
+	if (xfs_sb_has_incompat_log_feature(&mp->m_sb,
+					    XFS_SB_FEAT_INCOMPAT_SPINODES))
+		return;
+
+	spin_lock(&mp->m_sb_lock);
+	if (xfs_sb_has_incompat_log_feature(&mp->m_sb,
+					    XFS_SB_FEAT_INCOMPAT_SPINODES)) {
+		spin_unlock(&mp->m_sb_lock);
+		return;
+	}
+
+	mp->m_sb.sb_features_incompat |= XFS_SB_FEAT_INCOMPAT_SPINODES;
+	spin_unlock(&mp->m_sb_lock);
+	xfs_mod_sb(tp, XFS_SB_FEATURES_INCOMPAT);
+}
+
 /*
  * Allocate new inodes in the allocation group specified by agbp.
  * Return 0 for success, else error code.
@@ -631,6 +652,18 @@ xfs_ialloc_ag_alloc(
 		if (error)
 			return error;
 	}
+
+	/*
+	 * Set an incompat feature bit as old drivers can't parse sparse
+	 * records. Pre-sparse inode chunk drivers will include the
+	 * holemask in the higher order freecount bits, resulting in a
+	 * bogus value.
+	 *
+	 * XXX: when is this bit removed?
+	 */
+	if (xfs_inobt_issparse(&rec))
+		xfs_sbversion_add_spinodes(tp, args.mp);
+
 	/*
 	 * Log allocation group header fields
 	 */
-- 
1.8.3.1

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