Re: [PATCH v2] Btrfs: add label to snapshot and subvol

[Miao Xie <miaox@cn.fujitsu.com>]

Hi, Anand

On fri, 16 Nov 2012 12:52:25 +0800, Anand jain wrote:
> +static int btrfs_ioctl_subvol_getlabel(struct btrfs_root *root,
> +						void __user *arg)
> +{
> +	char *label;
> +
> +	label = btrfs_root_label(&root->root_item);
> +	if (copy_to_user(arg, label, BTRFS_SUBVOL_LABEL_SIZE))
> +		return -EFAULT;
> +	return 0;
> +}
> +
> +static int btrfs_ioctl_subvol_setlabel(struct btrfs_root *root,
> +						void __user *arg)
> +{
> +	char label[BTRFS_SUBVOL_LABEL_SIZE+1];
> +	struct btrfs_trans_handle *trans;
> +
> +	if (copy_from_user(label, arg, BTRFS_SUBVOL_LABEL_SIZE))
> +		return -EFAULT;
> +	trans = btrfs_join_transaction(root);
> +	if (IS_ERR(trans))
> +		return PTR_ERR(trans);
> +	btrfs_root_set_label(&root->root_item, label);
> +	btrfs_end_transaction(trans, root);

We need a lock to protect the label, and besides that, we need to get the write
access before we set the label for the subvolume.

Thanks
Miao