xfs: rename XFS_REFC_COW_START to _COWFLAG

We've been (ab)using XFS_REFC_COW_START as both an integer quantity and
a bit flag, even though it's *only* a bit flag. Rename the variable to
reflect its nature and update the cast target since we're not supposed
to be comparing it to xfs_agblock_t now.

Signed-off-by: Darrick J. Wong <[e-mail]>
Reviewed-by: Dave Chinner <[e-mail]>

fs/xfs/libxfs/xfs_format.h

···
  * on the startblock.  This speeds up mount time deletion of stale
  * staging extents because they're all at the right side of the tree.
  */
-#define XFS_REFC_COW_START		((xfs_agblock_t)(1U << 31))
+#define XFS_REFC_COWFLAG		(1U << 31)
 #define REFCNTBT_COWFLAG_BITLEN		1
 #define REFCNTBT_AGBLOCK_BITLEN		31
 

fs/xfs/libxfs/xfs_refcount.c

···
 	uint32_t			start;
 
 	start = be32_to_cpu(rec->refc.rc_startblock);
-	if (start & XFS_REFC_COW_START) {
-		start &= ~XFS_REFC_COW_START;
+	if (start & XFS_REFC_COWFLAG) {
+		start &= ~XFS_REFC_COWFLAG;
 		irec->rc_domain = XFS_REFC_DOMAIN_COW;
 	} else {
 		irec->rc_domain = XFS_REFC_DOMAIN_SHARED;
···
 	int				error;
 
 	/* reflink filesystems mustn't have AGs larger than 2^31-1 blocks */
-	BUILD_BUG_ON(XFS_MAX_CRC_AG_BLOCKS >= XFS_REFC_COW_START);
+	BUILD_BUG_ON(XFS_MAX_CRC_AG_BLOCKS >= XFS_REFC_COWFLAG);
 	if (mp->m_sb.sb_agblocks > XFS_MAX_CRC_AG_BLOCKS)
 		return -EOPNOTSUPP;
 

fs/xfs/libxfs/xfs_refcount.h

···
 	 * query functions (which set rc_domain == -1U), so we check that the
 	 * domain is /not/ shared.
 	 */
-	start = startblock & ~XFS_REFC_COW_START;
+	start = startblock & ~XFS_REFC_COWFLAG;
 	if (domain != XFS_REFC_DOMAIN_SHARED)
-		start |= XFS_REFC_COW_START;
+		start |= XFS_REFC_COWFLAG;
 
 	return start;
 }