xfs: don't allow reflink when the AG is low on space

If the AG free space is down to the reserves, refuse to reflink our
way out of space.  Hopefully userspace will make a real copy and/or go
elsewhere.

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

1 files changed, 35 insertions, 0 deletions

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 8e89411..e92ccd3 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -54,6 +54,8 @@
 #include "xfs_reflink.h"
 #include "xfs_iomap.h"
 #include "xfs_rmap_btree.h"
+#include "xfs_sb.h"
+#include "xfs_ag_resv.h"
 
 /*
  * Copy on Write of Shared Blocks
@@ -978,6 +980,31 @@ out_error:
 }
 
 /*
+ * Do we have enough reserve in this AG to handle a reflink?  The refcount
+ * btree already reserved all the space it needs, but the rmap btree can grow
+ * infinitely, so we won't allow more reflinks when the AG is down to the
+ * btree reserves.
+ */
+static int
+xfs_reflink_ag_has_free_space(
+	struct xfs_mount	*mp,
+	xfs_agnumber_t		agno)
+{
+	struct xfs_perag	*pag;
+	int			error = 0;
+
+	if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
+		return 0;
+
+	pag = xfs_perag_get(mp, agno);
+	if (xfs_ag_resv_critical(pag, XFS_AG_RESV_AGFL) ||
+	    xfs_ag_resv_critical(pag, XFS_AG_RESV_METADATA))
+		error = -ENOSPC;
+	xfs_perag_put(pag);
+	return error;
+}
+
+/*
  * Unmap a range of blocks from a file, then map other blocks into the hole.
  * The range to unmap is (destoff : destoff + srcioff + irec->br_blockcount).
  * The extent irec is mapped into dest at irec->br_startoff.
@@ -1009,6 +1036,14 @@ xfs_reflink_remap_extent(
 			irec->br_startblock != DELAYSTARTBLOCK &&
 			!ISUNWRITTEN(irec));
 
+	/* No reflinking if we're low on space */
+	if (real_extent) {
+		error = xfs_reflink_ag_has_free_space(mp,
+				XFS_FSB_TO_AGNO(mp, irec->br_startblock));
+		if (error)
+			goto out;
+	}
+
 	/* Start a rolling transaction to switch the mappings */
 	resblks = XFS_EXTENTADD_SPACE_RES(ip->i_mount, XFS_DATA_FORK);
 	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, 0, &tp);