Re: [RFC PATCH v1 2/2] xfs: don't set warns on the id==0 dquot

[Dave Chinner <david@fromorbit.com>]

On Thu, Apr 21, 2022 at 09:58:15AM -0700, Catherine Hoang wrote:
> Quotas are not enforced on the id==0 dquot, so the quota code uses it
> to store warning limits and timeouts.  Having just dropped support for
> warning limits, this field no longer has any meaning.  Return -EINVAL
> for this dquot id if the fieldmask has any of the QC_*_WARNS set.
> 
> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
> ---
>  fs/xfs/xfs_qm_syscalls.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/xfs/xfs_qm_syscalls.c b/fs/xfs/xfs_qm_syscalls.c
> index e7f3ac60ebd9..bdbd5c83b08e 100644
> --- a/fs/xfs/xfs_qm_syscalls.c
> +++ b/fs/xfs/xfs_qm_syscalls.c
> @@ -290,6 +290,8 @@ xfs_qm_scall_setqlim(
>  		return -EINVAL;
>  	if ((newlim->d_fieldmask & XFS_QC_MASK) == 0)
>  		return 0;
> +	if ((newlim->d_fieldmask & QC_WARNS_MASK) && id == 0)
> +		return -EINVAL;

Why would we do this for only id == 0? This will still allow
non-zero warning values to be written to dquots that have id != 0,
but I'm not sure why we'd allow this given that the previous
patch just removed all the warning limit checking?

Which then makes me ask: why are we still reading the warning counts
from on disk dquots and writing in-memory values back to dquots?
Shouldn't xfs_dquot_to_disk() just write zeros to the warning fields
now, and xfs_dquot_from_disk() elide reading the warning counts
altogether? i.e. can we remove d_bwarns, d_iwarns and d_rtbwarns
from the struct fs_disk_quota altogether now?

Which then raises the question of whether copy_from_xfs_dqblk() and
friends should still support warn counts up in fs/quota/quota.c...?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com