verity: handle trees with an odd node count correctly

dm-bht.c

  /*
  * Copyright (C) 2010 The Chromium OS Authors <chromium-os-dev@chromium.org>
  *
  * Device-Mapper block hash tree interface.
  * See Documentation/device-mapper/dm-bht.txt for details.
  *
  * This file is released under the GPL.
  */
 
 #include <asm/atomic.h>
@@ skipping 816 matching lines @@
  */
 int dm_bht_compute(struct dm_bht *bht, void *read_cb_ctx)
 {
         int depth, r;
 
         for (depth = bht->depth - 2; depth >= 0; depth--) {
                 struct dm_bht_level *level = dm_bht_get_level(bht, depth);
                 struct dm_bht_level *child_level = level + 1;
                 struct dm_bht_entry *entry = level->entries;
                 struct dm_bht_entry *child = child_level->entries;
-                unsigned int count = min(bht->node_count, child_level->count);
                 unsigned int i, j;
 
                 r = dm_bht_maybe_read_entries(bht, read_cb_ctx, depth,
                                               0, level->count, true);
                 if (r < 0) {
                         DMCRIT("an error occurred while reading entry");
                         goto out;
                 }
 
                 for (i = 0; i < level->count; i++, entry++) {
+                        unsigned int count = bht->node_count;
+                        if (i == (level->count - 1))

[Will Drewry, 2011/03/25 02:52:49]

Could this just be:
unsigned int count = child_level->count % bht->node_count;
if (count == 0)
  count = bht->node_count;

?

+                                count = child_level->count % bht->node_count;
+                        if (count == 0)
+                                count = bht->node_count;
                         for (j = 0; j < count; j++, child++) {
                                 u8 *block = child->nodes;
                                 u8 *digest = dm_bht_node(bht, entry, j);
 
                                 r = dm_bht_compute_hash(bht, block, digest);
                                 if (r) {
                                         DMERR("Failed to update (d=%u,i=%u)",
                                               depth, i);
                                         goto out;
                                 }
@@ skipping 329 matching lines @@
                 DMERR("no root digest exists to export");
                 if (available > 0)
                         *hexdigest = 0;
                 return -1;
         }
         dm_bht_bin_to_hex(bht->root_digest, hexdigest, bht->digest_size);
         return 0;
 }
 EXPORT_SYMBOL(dm_bht_root_hexdigest);