Re: [RFC PATCH V6 2/2] Btrfs: Add a new ioctl to change the label of a mounted file system

[Jeff Liu <jeff.liu@oracle.com>]

On 12/19/2012 10:21 PM, David Sterba wrote:
> On Tue, Dec 18, 2012 at 11:06:07AM +0800, Jeff Liu wrote:
>> +static int btrfs_ioctl_set_fslabel(struct file *file, void __user *arg)
>> +{
>> +	struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
>> +	struct btrfs_super_block *super_block = root->fs_info->super_copy;
>> +	struct btrfs_trans_handle *trans;
>> +	char label[BTRFS_LABEL_SIZE];
>> +	int ret;
>> +
>> +	if (!capable(CAP_SYS_ADMIN))
>> +		return -EPERM;
>> +
>> +	if (copy_from_user(label, arg, sizeof(label)))
>> +		return -EFAULT;
>> +
>> +	if (strnlen(label, BTRFS_LABEL_SIZE) == BTRFS_LABEL_SIZE)
>> +		return -EINVAL;
>> +
>> +	ret = mnt_want_write_file(file);
>> +	if (ret)
>> +		return ret;
>> +
>> +	mutex_lock(&root->fs_info->volume_mutex);
>> +	trans = btrfs_start_transaction(root, 1);
>> +	if (IS_ERR(trans)) {
>> +		ret = PTR_ERR(trans);
>> +		goto out_unlock;
>> +	}
>> +
>> +	strcpy(super_block->label, label);
>> +	btrfs_end_transaction(trans, root);
> 
> If this fails, eg. with EIO, it will not be reported back to the user
> 
>         ret = btrfs_end_transaction(trans, root);
> 
> should fix it.
Thank you, I'll send out a revised version after a little while.

-Jeff
> 
>> +
>> +out_unlock:
>> +	mutex_unlock(&root->fs_info->volume_mutex);
>> +	mnt_drop_write_file(file);
>> +	return ret;
>> +}
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