Add inode space usage statistics tracking to blockstore

src/blockstore.h

@@ -183,6 +183,9 @@ public:
     // Unstable writes are added here (map of object_id -> version)
     std::unordered_map<object_id, uint64_t> & get_unstable_writes();
 
+    // Get per-inode space usage statistics
+    std::map<uint64_t, int64_t> & get_inode_space_stats();
+
     // FIXME rename to object_size
     uint32_t get_block_size();
     uint64_t get_block_count();