xfs: refactor delalloc indlen reservation split into helper

The delayed allocation indirect reservation splitting code is not
sufficient in some cases where a delalloc extent is split in two. In
preparation for enhancements to this code, refactor the current indlen
distribution algorithm into a new helper function.

[dchinner: rename temp, temp2 variables]

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
index b48abc3..6de613b 100644 (file)
--- a/fs/xfs/libxfs/xfs_bmap.c
+++ b/fs/xfs/libxfs/xfs_bmap.c
@@ -4720,6 +4720,47 @@ error0:
        return error;
 }
 
+/*
+ * When a delalloc extent is split (e.g., due to a hole punch), the original
+ * indlen reservation must be shared across the two new extents that are left
+ * behind.
+ *
+ * Given the original reservation and the worst case indlen for the two new
+ * extents (as calculated by xfs_bmap_worst_indlen()), split the original
+ * reservation fairly across the two new extents.
+ */
+static void
+xfs_bmap_split_indlen(
+       xfs_filblks_t                   ores,           /* original res. */
+       xfs_filblks_t                   *indlen1,       /* ext1 worst indlen */
+       xfs_filblks_t                   *indlen2)       /* ext2 worst indlen */
+{
+       xfs_filblks_t                   len1 = *indlen1;
+       xfs_filblks_t                   len2 = *indlen2;
+       xfs_filblks_t                   nres = len1 + len2; /* new total res. */
+
+       /*
+        * The only blocks available are those reserved for the original extent.
+        * Therefore, we have to skim blocks off each of the new reservations so
+        * long as the new total reservation is greater than the original.
+        */
+       while (nres > ores) {
+               if (len1) {
+                       len1--;
+                       nres--;
+               }
+               if (nres == ores)
+                       break;
+               if (len2) {
+                       len2--;
+                       nres--;
+               }
+       }
+
+       *indlen1 = len1;
+       *indlen2 = len2;
+}
+
 /*
  * Called by xfs_bmapi to update file extent records and the btree
  * after removing space (or undoing a delayed allocation).
@@ -4985,27 +5026,21 @@ xfs_bmap_del_extent(
                                XFS_IFORK_NEXTENTS(ip, whichfork) + 1);
                } else {
                        ASSERT(whichfork == XFS_DATA_FORK);
-                       temp = xfs_bmap_worst_indlen(ip, temp);
+
+                       /*
+                        * Distribute the original indlen reservation across the
+                        * two new extents.
+                        */
+                       temp = xfs_bmap_worst_indlen(ip, got.br_blockcount);
+                       temp2 = xfs_bmap_worst_indlen(ip, new.br_blockcount);
+                       xfs_bmap_split_indlen(da_old, &temp, &temp2);
+                       da_new = temp + temp2;
+
+                       /*
+                        * Set the reservation for each extent.
+                        */
                        xfs_bmbt_set_startblock(ep, nullstartblock((int)temp));
-                       temp2 = xfs_bmap_worst_indlen(ip, temp2);
                        new.br_startblock = nullstartblock((int)temp2);
-                       da_new = temp + temp2;
-                       while (da_new > da_old) {
-                               if (temp) {
-                                       temp--;
-                                       da_new--;
-                                       xfs_bmbt_set_startblock(ep,
-                                               nullstartblock((int)temp));
-                               }
-                               if (da_new == da_old)
-                                       break;
-                               if (temp2) {
-                                       temp2--;
-                                       da_new--;
-                                       new.br_startblock =
-                                               nullstartblock((int)temp2);
-                               }
-                       }
                }
                trace_xfs_bmap_post_update(ip, *idx, state, _THIS_IP_);
                xfs_iext_insert(ip, *idx + 1, 1, &new, state);