Just getting up to speed on this patch, so only a few cosmetic
comments so far:

+		if (ap->flags & XFS_BMAPI_COWFORK) {
+			xfs_bmap_btalloc_quota_cow(ap, &args);
+		} else {
+			ap->ip->i_d.di_nblocks += args.len;
+			xfs_trans_log_inode(ap->tp, ap->ip, XFS_ILOG_CORE);
+			/*
+			 * Adjust the disk quota also. This was reserved
+			 * earlier.
+			 */
+			xfs_trans_mod_dquot_byino(ap->tp, ap->ip,
+				ap->wasdel ? XFS_TRANS_DQ_DELBCOUNT :
+						XFS_TRANS_DQ_BCOUNT,
+				(long) args.len);
+		}

Shouldn't we instead have a helper for the whole above section?