Re: [PATCH v2 2/2] xfs: add FS_IOC_GETFSUUID ioctl

[Dave Chinner <david@fromorbit.com>]

On Fri, Nov 18, 2022 at 01:14:08PM -0800, Catherine Hoang wrote:
> Add a new ioctl to retrieve the UUID of a mounted xfs filesystem. This is a
> precursor to adding the SETFSUUID ioctl.
> 
> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
> Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
> ---
>  fs/xfs/xfs_ioctl.c | 36 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 1f783e979629..cf77715afe9e 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1865,6 +1865,39 @@ xfs_fs_eofblocks_from_user(
>  	return 0;
>  }
>  
> +static int
> +xfs_ioctl_getuuid(
> +	struct xfs_mount	*mp,
> +	struct fsuuid __user	*ufsuuid)
> +{
> +	struct fsuuid		fsuuid;
> +	__u8			uuid[UUID_SIZE];

uuid_t, please, not an open coded uuid_t.

> +
> +	if (copy_from_user(&fsuuid, ufsuuid, sizeof(fsuuid)))
> +		return -EFAULT;

I still think this failing to copy the flex array member and then
having to declare a local uuid buffer is an ugly wart, not just on
the API side of things.

> +	if (fsuuid.fsu_len == 0) {
> +		fsuuid.fsu_len = UUID_SIZE;

XFS uses sizeof(uuid_t) for the size of it's uuids, not UUID_SIZE.

> +		if (copy_to_user(&ufsuuid->fsu_len, &fsuuid.fsu_len,
> +					sizeof(fsuuid.fsu_len)))
> +			return -EFAULT;
> +		return 0;
> +	}
> +
> +	if (fsuuid.fsu_len < UUID_SIZE || fsuuid.fsu_flags != 0)
> +		return -EINVAL;
> +
> +	spin_lock(&mp->m_sb_lock);
> +	memcpy(uuid, &mp->m_sb.sb_uuid, UUID_SIZE);
> +	spin_unlock(&mp->m_sb_lock);

Hmmmm. Shouldn't we be promoting xfs_fs_get_uuid() to xfs_super.c
(without the pNFS warning!) and calling that here, rather than open
coding another "get the XFS superblock UUID" function here?

i.e.
	if (fsuuid.fsu_flags != 0)
		return -EINVAL;

	error = xfs_fs_get_uuid(&mp->m_sb, uuid, &fsuuid.fsu_len, NULL);
	if (error)
		return -EINVAL;

Also, uuid_copy()?

Cheers,

Dave.

-- 
Dave Chinner
david@fromorbit.com