xfs: treat CoW fork operations as delalloc for quota accounting

Since the CoW fork only exists in memory, it is incorrect to update the
on-disk quota block counts when we modify the CoW fork.  Unlike the data
fork, even real extents in the CoW fork are only delalloc-style
reservations (on-disk they're owned by the refcountbt) so they must not
be tracked in the on disk quota info.  Ensure the i_delayed_blks
accounting reflects this too.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_bmap.c

@@ -3343,8 +3343,35 @@ xfs_bmap_btalloc_accounting(
 	struct xfs_bmalloca	*ap,
 	struct xfs_alloc_arg	*args)
 {
-	if (!(ap->flags & XFS_BMAPI_COWFORK))
-		ap->ip->i_d.di_nblocks += args->len;
+	if (ap->flags & XFS_BMAPI_COWFORK) {
+		/*
+		 * COW fork blocks are in-core only and thus are treated as
+		 * in-core quota reservation (like delalloc blocks) even when
+		 * converted to real blocks. The quota reservation is not
+		 * accounted to disk until blocks are remapped to the data
+		 * fork. So if these blocks were previously delalloc, we
+		 * already have quota reservation and there's nothing to do
+		 * yet.
+		 */
+		if (ap->wasdel)
+			return;
+
+		/*
+		 * Otherwise, we've allocated blocks in a hole. The transaction
+		 * has acquired in-core quota reservation for this extent.
+		 * Rather than account these as real blocks, however, we reduce
+		 * the transaction quota reservation based on the allocation.
+		 * This essentially transfers the transaction quota reservation
+		 * to that of a delalloc extent.
+		 */
+		ap->ip->i_delayed_blks += args->len;
+		xfs_trans_mod_dquot_byino(ap->tp, ap->ip, XFS_TRANS_DQ_RES_BLKS,
+				-(long)args->len);
+		return;
+	}
+
+	/* data/attr fork only */
+	ap->ip->i_d.di_nblocks += args->len;
 	xfs_trans_log_inode(ap->tp, ap->ip, XFS_ILOG_CORE);
 	if (ap->wasdel)
 		ap->ip->i_delayed_blks -= args->len;
@@ -4820,6 +4847,7 @@ xfs_bmap_del_extent_cow(
 		xfs_iext_insert(ip, icur, &new, state);
 		break;
 	}
+	ip->i_delayed_blks -= del->br_blockcount;
 }
 
 /*

fs/xfs/xfs_reflink.c

@@ -599,10 +599,6 @@ xfs_reflink_cancel_cow_blocks(
 					del.br_startblock, del.br_blockcount,
 					NULL);
 
-			/* Update quota accounting */
-			xfs_trans_mod_dquot_byino(*tpp, ip, XFS_TRANS_DQ_BCOUNT,
-					-(long)del.br_blockcount);
-
 			/* Roll the transaction */
 			xfs_defer_ijoin(&dfops, ip);
 			error = xfs_defer_finish(tpp, &dfops);
@@ -613,6 +609,13 @@ xfs_reflink_cancel_cow_blocks(
 
 			/* Remove the mapping from the CoW fork. */
 			xfs_bmap_del_extent_cow(ip, &icur, &got, &del);
+
+			/* Remove the quota reservation */
+			error = xfs_trans_reserve_quota_nblks(NULL, ip,
+					-(long)del.br_blockcount, 0,
+					XFS_QMOPT_RES_REGBLKS);
+			if (error)
+				break;
 		} else {
 			/* Didn't do anything, push cursor back. */
 			xfs_iext_prev(ifp, &icur);
@@ -795,6 +798,10 @@ xfs_reflink_end_cow(
 		if (error)
 			goto out_defer;
 
+		/* Charge this new data fork mapping to the on-disk quota. */
+		xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_DELBCOUNT,
+				(long)del.br_blockcount);
+
 		/* Remove the mapping from the CoW fork. */
 		xfs_bmap_del_extent_cow(ip, &icur, &got, &del);