Re: [PATCH v4] btrfs: Remove received_uuid during received snapshot ro->rw switch

[Anand Jain <anand.jain@oracle.com>]

On 10/05/2017 04:22 PM, Nikolay Borisov wrote:
> Currently when a read-only snapshot is received and subsequently its ro property
> is set to false i.e. switched to rw-mode the received_uuid of that subvol remains
> intact. However, once the received volume is switched to RW mode we cannot
> guaranteee that it contains the same data, so it makes sense to remove the
> received uuid. The presence of the received_uuid can also cause problems when
> the volume is being send.


Wonder if this [1] approach was considered
[1]
  - set a flag on the subvolume to indicate its dirtied so that 
received_uuid can be kept forever just in case if user needs it for some 
reference at a later point of time.

Thanks, Anand


> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> Suggested-by: David Sterba <dsterba@suse.cz>
> ---
> 
> v4:
>   * Put the uuid tree removal code after the lightweight 'send in progress'
>   check and don't move btrfs_start_transaction as suggested by David
>   
> v3:
>   * Rework the patch considering latest feedback from David Sterba i.e.
>    explicitly use btrfs_end_transaction
> 
>   fs/btrfs/ioctl.c | 20 ++++++++++++++++++++
>   1 file changed, 20 insertions(+)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index ee4ee7cbba72..9328c091854b 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -1775,6 +1775,7 @@ static noinline int btrfs_ioctl_subvol_setflags(struct file *file,
>   	struct btrfs_trans_handle *trans;
>   	u64 root_flags;
>   	u64 flags;
> +	bool clear_received_uuid = false;
>   	int ret = 0;
>   
>   	if (!inode_owner_or_capable(inode))
> @@ -1824,6 +1825,7 @@ static noinline int btrfs_ioctl_subvol_setflags(struct file *file,
>   			btrfs_set_root_flags(&root->root_item,
>   				     root_flags & ~BTRFS_ROOT_SUBVOL_RDONLY);
>   			spin_unlock(&root->root_item_lock);
> +			clear_received_uuid = true;
>   		} else {
>   			spin_unlock(&root->root_item_lock);
>   			btrfs_warn(fs_info,
> @@ -1840,6 +1842,24 @@ static noinline int btrfs_ioctl_subvol_setflags(struct file *file,
>   		goto out_reset;
>   	}
>   
> +	if (clear_received_uuid) {
> +	        if (!btrfs_is_empty_uuid(root->root_item.received_uuid)) {
> +	                ret = btrfs_uuid_tree_rem(trans, fs_info,
> +	                                root->root_item.received_uuid,
> +	                                BTRFS_UUID_KEY_RECEIVED_SUBVOL,
> +	                                root->root_key.objectid);
> +
> +	                if (ret && ret != -ENOENT) {
> +	                        btrfs_abort_transaction(trans, ret);
> +	                        btrfs_end_transaction(trans);
> +	                        goto out_reset;
> +	                }
> +
> +	                memset(root->root_item.received_uuid, 0,
> +	                                BTRFS_UUID_SIZE);
> +	        }
> +	}
> +
>   	ret = btrfs_update_root(trans, fs_info->tree_root,
>   				&root->root_key, &root->root_item);
>   	if (ret < 0) {
>