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>

diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 8e894118295fec9154adc520abe814d931c7b74a..e92ccd3163916426ff7dc37694416c6a4794795f 100644 (file)
--- 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
@@ -977,6 +979,31 @@ out_error:
        return 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).
@@ -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);