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Date:   Thu, 08 Feb 2018 17:38:24 -0700
From:   Dave Jiang <>
Subject: [PATCH v3 3/3] xfs: reject removal of realtime flag when datadev
 doesn't support DAX

In a situation where the rt_dev is DAX and data_dev is not DAX, if the user
requests to remove the realtime flag via ioctl we can no longer support DAX
for that file. Dynamic changing of S_DAX on the inode is not supported due
to various complications in the existing implementation. Therefore until we
address the dynamic S_DAX change issues, we must disallow realtime flag
being removed.

Signed-off-by: Dave Jiang <>
 fs/xfs/xfs_ioctl.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index e440d789ed1b..cd5a5c61da39 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1029,6 +1029,21 @@ xfs_ioctl_setattr_xflags(
 	struct xfs_mount	*mp = ip->i_mount;
 	uint64_t		di_flags2;
+	struct inode		*inode = VFS_I(ip);
+	struct super_block	*sb = inode->i_sb;
+	/*
+	 * In the case that the inode is realtime, and we are trying to remove
+	 * the realtime flag, and the rtdev supports DAX but the datadev does
+	 * not support DAX, we can't allow the realtime flag to be removed
+	 * since we do not support dynamic S_DAX flag removal yet.
+	 */
+	if ((XFS_IS_REALTIME_INODE(ip)) &&
+	    !(fa->fsx_xflags & FS_XFLAG_REALTIME) &&
+	    bdev_dax_supported(sb, mp->m_rtdev_targp->bt_bdev,
+		    sb->s_blocksize) &&
+	    !bdev_dax_supported(sb, mp->m_ddev_targp->bt_bdev, sb->s_blocksize))
+		return -ENOTSUPP;
 	/* Can't change realtime flag if any extents are allocated. */
 	if ((ip->i_d.di_nextents || ip->i_delayed_blks) &&

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