Double-check for double-alloc bugs

src/blockstore_write.cpp

@@ -268,6 +268,16 @@ int blockstore_impl_t::dequeue_write(blockstore_op_t *op)
             cancel_all_writes(op, dirty_it, -ENOSPC);
             return 2;
         }
+#ifndef NDEBUG
+        // Double-check to not overwrite anything if easily possible
+        if (inmemory_meta)
+        {
+            uint64_t sector = (loc / (meta_block_size / clean_entry_size)) * meta_block_size;
+            uint64_t pos = (loc % (meta_block_size / clean_entry_size));
+            clean_disk_entry *meta_entry = (clean_disk_entry*)(metadata_buffer + sector + pos*clean_entry_size);
+            assert(!meta_entry->oid.inode);
+        }
+#endif
         write_iodepth++;
         BS_SUBMIT_GET_SQE(sqe, data);
         dirty_it->second.location = loc << block_order;