[PATCH 2/2] xfs: only set extent size hint when asked

[Iustin Pop]

On Tue, Sep 30, 2014 at 11:46:05AM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner at redhat.com>
> 
> Currently the extent size hint is set unconditionally in
> xfs_ioctl_setattr(), even when the FSX_EXTSIZE flag is not set. This
> means we can set values from uninitialised stack variables. Hence
> only set the extent size hint from userspace when both the mask
> falg is set and the inode has the XFS_DIFLAG_EXTSIZE flag set to
> indicate that we should have an extent size hint set on the inode.
> 
> Signed-off-by: Dave Chinner <dchinner at redhat.com>
> ---
>  fs/xfs/xfs_ioctl.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 87c3bd1..24c926b 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1231,13 +1231,25 @@ xfs_ioctl_setattr(
>  
>  	}
>  
> -	if (mask & FSX_EXTSIZE)
> -		ip->i_d.di_extsize = fa->fsx_extsize >> mp->m_sb.sb_blocklog;
>  	if (mask & FSX_XFLAGS) {
>  		xfs_set_diflags(ip, fa->fsx_xflags);
>  		xfs_diflags_to_linux(ip);
>  	}
>  
> +	/*
> +	 * Only set the extent size hint if we've already determined that the
> +	 * extent size hint should be set on the inode. If no extent size flags
> +	 * are set on the inode then unconditionally clear the extent size hint.
> +	 */
> +	if (mask & FSX_EXTSIZE) {
> +		int	extsize = 0;
> +
> +		if (ip->i_d.di_flags &
> +				(XFS_DIFLAG_EXTSIZE | XFS_DIFLAG_EXTSZINHERIT))
> +			extsize = fa->fsx_extsize >> mp->m_sb.sb_blocklog;
> +		ip->i_d.di_extsize = extsize;

Quick question: this sounds sane, but it will have the following effect
(if I understand things correctly): updating other flags on the inode
(e.g. XFS_XFLAG_NOATIME) might change the recorded extent size. True, it
will correct the size if not appropriate and it will have a noop impact,
but still it will be an unrelated inode change. Would it make sense to
document this in the xfsctl man page then?

thanks,
iustin