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Date: Mon, 17 Dec 2012 19:57:28 +0800
From: Miao Xie <miaox@cn.fujitsu.com>
Reply-To: miaox@cn.fujitsu.com
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To: Jeff Liu <jeff.liu@oracle.com>
CC: linux-btrfs@vger.kernel.org, anand.jain@oracle.com
Subject: Re: [RFC PATCH V5 2/2] Btrfs: Add a new ioctl to change the label
 of a mounted file system
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References: <50CF0063.3060503@oracle.com>

On 	mon, 17 Dec 2012 19:22:11 +0800, Jeff Liu wrote:
> Introduce a new ioctl BTRFS_IOC_SET_FSLABEL to change the label of a mounted file system.
> 
> Signed-off-by: Jie Liu <jeff.liu@oracle.com>
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> Cc: Miao Xie <miaox@cn.fujitsu.com>
> 
> ---
>  fs/btrfs/ioctl.c |   40 ++++++++++++++++++++++++++++++++++++++++
>  fs/btrfs/ioctl.h |    2 ++
>  2 files changed, 42 insertions(+)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 6a2488a..0186651 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3712,6 +3712,44 @@ static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
>  	return ret ? -EFAULT : 0;
>  }
>  
> +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;
> +	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 (strlen(label) > BTRFS_LABEL_SIZE - 1)
> +		return -EINVAL;

I think we should use strnlen()

Thanks
Miao

> +
> +	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;
> +	}
> +
> +	label[BTRFS_LABEL_SIZE - 1] = '\0';
> +	strcpy(super_block->label, label);
> +	btrfs_end_transaction(trans, root);
> +
> +out_unlock:
> +	mutex_unlock(&root->fs_info->volume_mutex);
> +	mnt_drop_write_file(file);
> +	return ret;
> +}
> +
>  long btrfs_ioctl(struct file *file, unsigned int
>  		cmd, unsigned long arg)
>  {
> @@ -3812,6 +3850,8 @@ long btrfs_ioctl(struct file *file, unsigned int
>  		return btrfs_ioctl_qgroup_limit(root, argp);
>  	case BTRFS_IOC_GET_FSLABEL:
>  		return btrfs_ioctl_get_fslabel(file, argp);
> +	case BTRFS_IOC_SET_FSLABEL:
> +		return btrfs_ioctl_set_fslabel(file, argp);
>  	}
>  
>  	return -ENOTTY;
> diff --git a/fs/btrfs/ioctl.h b/fs/btrfs/ioctl.h
> index 5b2cbef..2abe239 100644
> --- a/fs/btrfs/ioctl.h
> +++ b/fs/btrfs/ioctl.h
> @@ -453,6 +453,8 @@ struct btrfs_ioctl_send_args {
>  			       struct btrfs_ioctl_qgroup_limit_args)
>  #define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
>  				   char[BTRFS_LABEL_SIZE])
> +#define BTRFS_IOC_SET_FSLABEL _IOW(BTRFS_IOCTL_MAGIC, 50, \
> +				   char[BTRFS_LABEL_SIZE])
>  #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
>  				      struct btrfs_ioctl_get_dev_stats)
>  #endif
>