Re: [PATCH] btrfs: qgroup: Automatically remove qgroup item when dropping a subvolume

[Josef Bacik <josef@toxicpanda.com>]

On 10/17/19 3:36 AM, Qu Wenruo wrote:
> [BUG]
> When a subvolume is created, we automatically create a level 0 qgroup
> for it, but don't remove it when the subvolume is dropped.
> 
> Although it's not a big deal, it can easily pollute the output of
> "btrfs qgroup show" and make it pretty annoying.
> 
> [FIX]
> For btrfs_drop_snapshot(), if it's a valid subvolume (not a reloc tree)
> and qgroup is enabled, we do the following work to remove the qgroup:
> - Commit transaction
>    This is to ensure that the qgroup numbers of that subvolume is updated
>    properly (all number of that subvolume should be 0).
> 
> - Start a new transaction for later operation
> 
> - Call btrfs_remove_qgroup()
> 
> So that qgroup can be automatically removed when the subvolume get fully
> dropped.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   fs/btrfs/extent-tree.c | 25 +++++++++++++++++++++++++
>   1 file changed, 25 insertions(+)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 49cb26fa7c63..5e8569cad16d 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -5182,6 +5182,7 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
>   	struct btrfs_root_item *root_item = &root->root_item;
>   	struct walk_control *wc;
>   	struct btrfs_key key;
> +	u64 rootid = root->root_key.objectid;
>   	int err = 0;
>   	int ret;
>   	int level;
> @@ -5384,6 +5385,30 @@ int btrfs_drop_snapshot(struct btrfs_root *root,
>   	}
>   	root_dropped = true;
>   out_end_trans:
> +	/* If qgroup is enabled, also try to remove the qgroup */
> +	if (test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags) && root_dropped &&
> +	    is_fstree(rootid) && !for_reloc) {


Is the !for_reloc check superflous here?  is_fstree() should be enough.  Thanks,

Josef