+static u64 div_factor(u64 num, int factor)
+{
+ if (factor == 10)
+ return num;
+ num *= factor;
+ do_div(num, 10);
+ return num;
+}
+
+
+int btrfs_balance(struct btrfs_root *dev_root)
+{
+ int ret;
+ struct list_head *cur;
+ struct list_head *devices = &dev_root->fs_info->fs_devices->devices;
+ struct btrfs_device *device;
+ u64 old_size;
+ u64 size_to_free;
+ struct btrfs_path *path;
+ struct btrfs_key key;
+ struct btrfs_chunk *chunk;
+ struct btrfs_root *chunk_root = dev_root->fs_info->chunk_root;
+ struct btrfs_trans_handle *trans;
+ struct btrfs_key found_key;
+
+
+ dev_root = dev_root->fs_info->dev_root;
+
+ mutex_lock(&dev_root->fs_info->fs_mutex);
+ /* step one make some room on all the devices */
+ list_for_each(cur, devices) {
+ device = list_entry(cur, struct btrfs_device, dev_list);
+ old_size = device->total_bytes;
+ size_to_free = div_factor(old_size, 1);
+ size_to_free = min(size_to_free, (u64)1 * 1024 * 1024);
+ if (device->total_bytes - device->bytes_used > size_to_free)
+ continue;
+
+ ret = btrfs_shrink_device(device, old_size - size_to_free);
+ BUG_ON(ret);
+
+ trans = btrfs_start_transaction(dev_root, 1);
+ BUG_ON(!trans);
+
+ ret = btrfs_grow_device(trans, device, old_size);
+ BUG_ON(ret);
+
+ btrfs_end_transaction(trans, dev_root);
+ }
+
+ /* step two, relocate all the chunks */
+ path = btrfs_alloc_path();
+ BUG_ON(!path);
+
+ key.objectid = BTRFS_FIRST_CHUNK_TREE_OBJECTID;
+ key.offset = (u64)-1;
+ key.type = BTRFS_CHUNK_ITEM_KEY;
+
+ while(1) {
+ ret = btrfs_search_slot(NULL, chunk_root, &key, path, 0, 0);
+ if (ret < 0)
+ goto error;
+
+ /*
+ * this shouldn't happen, it means the last relocate
+ * failed
+ */
+ if (ret == 0)
+ break;
+
+ ret = btrfs_previous_item(chunk_root, path, 0,
+ BTRFS_CHUNK_ITEM_KEY);
+ if (ret) {
+ break;
+ }
+ btrfs_item_key_to_cpu(path->nodes[0], &found_key,
+ path->slots[0]);
+ if (found_key.objectid != key.objectid)
+ break;
+ chunk = btrfs_item_ptr(path->nodes[0],
+ path->slots[0],
+ struct btrfs_chunk);
+ key.offset = found_key.offset;
+ /* chunk zero is special */
+ if (key.offset == 0)
+ break;
+
+ ret = btrfs_relocate_chunk(chunk_root,
+ chunk_root->root_key.objectid,
+ found_key.objectid,
+ found_key.offset);
+ BUG_ON(ret);
+ btrfs_release_path(chunk_root, path);
+ }
+ ret = 0;
+error:
+ btrfs_free_path(path);
+ mutex_unlock(&dev_root->fs_info->fs_mutex);
+ return ret;
+}
+