XFS_REFC_COWFLAG
if (start & XFS_REFC_COWFLAG) {
start &= ~XFS_REFC_COWFLAG;
BUILD_BUG_ON(XFS_MAX_RGBLOCKS >= XFS_REFC_COWFLAG);
BUILD_BUG_ON(XFS_MAX_CRC_AG_BLOCKS >= XFS_REFC_COWFLAG);
start = startblock & ~XFS_REFC_COWFLAG;
start |= XFS_REFC_COWFLAG;
start = irec->rc_startblock & ~XFS_REFC_COWFLAG;
start |= XFS_REFC_COWFLAG;
start = irec->rc_startblock & ~XFS_REFC_COWFLAG;
start |= XFS_REFC_COWFLAG;