Re: [PATCH V2] xfs: do not allow reflinking inodes with the dax flag set

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Jan 07, 2021 at 03:36:34PM -0600, Eric Sandeen wrote:
> Today, xfs_reflink_remap_prep() will reject inodes which are in the CPU
> direct access state, i.e. IS_DAX() is true.  However, it is possible to
> have inodes with the XFS_DIFLAG2_DAX set, but which are not activated as
> dax, due to the flag being set after the inode was loaded.
> 
> To avoid confusion and make the lack of dax+reflink crystal clear for the
> user, reject reflink requests for both IS_DAX and XFS_DIFLAG2_DAX inodes
> unless DAX mode is impossible due to mounting with -o dax=never.

I thought we were allowing arbitrary combinations of DAX & REFLINK inode
flags now, since we're now officially ok with "you set the inode flag
but you don't get cpu direct access because $reasons"?

--D

> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> V2: Allow reflinking dax-flagged inodes in "mount -o dax=never" mode
> 
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 6fa05fb78189..e238a5b7b722 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -1308,6 +1308,15 @@ xfs_reflink_remap_prep(
>  	if (IS_DAX(inode_in) || IS_DAX(inode_out))
>  		goto out_unlock;
>  
> +	/*
> +	 * Until we have dax+reflink, don't allow reflinking dax-flagged
> +	 * inodes unless we are in dax=never mode.
> +	 */
> +	if (!(mp->m_flags & XFS_MOUNT_DAX_NEVER) &&
> +	     (src->i_d.di_flags2 & XFS_DIFLAG2_DAX ||
> +	      dest->i_d.di_flags2 & XFS_DIFLAG2_DAX))
> +		goto out_unlock;
> +
>  	ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
>  			len, remap_flags);
>  	if (ret || *len == 0)
>