fs/xfs: Create function xfs_inode_should_enable_dax()

xfs_inode_supports_dax() should reflect if the inode can support DAX not
that it is enabled for DAX.

Change the use of xfs_inode_supports_dax() to reflect only if the inode
and underlying storage support dax.

Add a new function xfs_inode_should_enable_dax() which reflects if the
inode should be enabled for DAX.
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_iops.c

@@ -1238,13 +1238,12 @@ xfs_inode_supports_dax(
 {
 	struct xfs_mount	*mp = ip->i_mount;
 
-	/* Only supported on non-reflinked files. */
-	if (!S_ISREG(VFS_I(ip)->i_mode) || xfs_is_reflink_inode(ip))
+	/* Only supported on regular files. */
+	if (!S_ISREG(VFS_I(ip)->i_mode))
 		return false;
 
-	/* DAX mount option or DAX iflag must be set. */
-	if (!(mp->m_flags & XFS_MOUNT_DAX_ALWAYS) &&
-	    !(ip->i_d.di_flags2 & XFS_DIFLAG2_DAX))
+	/* Only supported on non-reflinked files. */
+	if (xfs_is_reflink_inode(ip))
 		return false;
 
 	/* Block size must match page size */
@@ -1255,6 +1254,23 @@ xfs_inode_supports_dax(
 	return xfs_inode_buftarg(ip)->bt_daxdev != NULL;
 }
 
+static bool
+xfs_inode_should_enable_dax(
+	struct xfs_inode *ip)
+{
+	if (!IS_ENABLED(CONFIG_FS_DAX))
+		return false;
+	if (ip->i_mount->m_flags & XFS_MOUNT_DAX_NEVER)
+		return false;
+	if (!xfs_inode_supports_dax(ip))
+		return false;
+	if (ip->i_mount->m_flags & XFS_MOUNT_DAX_ALWAYS)
+		return true;
+	if (ip->i_d.di_flags2 & XFS_DIFLAG2_DAX)
+		return true;
+	return false;
+}
+
 STATIC void
 xfs_diflags_to_iflags(
 	struct inode		*inode,
@@ -1273,7 +1289,7 @@ xfs_diflags_to_iflags(
 		inode->i_flags |= S_SYNC;
 	if (flags & XFS_DIFLAG_NOATIME)
 		inode->i_flags |= S_NOATIME;
-	if (xfs_inode_supports_dax(ip))
+	if (xfs_inode_should_enable_dax(ip))
 		inode->i_flags |= S_DAX;
 }