netdev - Re: [RFC 1/2] net/ethtool: Add new coalescing parameter for queue

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Date:	Tue, 08 Dec 2015 19:00:52 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Shannon Nelson <shannon.nelson@...el.com>, kan.liang@...el.com
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
	bwh@...nel.org, Jesse Brandeburg <jesse.brandeburg@...el.com>,
	andi@...stfloor.org, f.fainelli@...il.com,
	alexander.duyck@...il.com,
	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	carolyn.wyborny@...el.com, donald.c.skidmore@...el.com,
	mitch.a.williams@...el.com, ogerlitz@...lanox.com,
	edumazet@...gle.com, jiri@...lanox.com, sfeldma@...il.com,
	gospo@...ulusnetworks.com, sasha.levin@...cle.com,
	dsahern@...il.com, tj@...nel.org, cascardo@...hat.com,
	corbet@....net
Subject: Re: [RFC 1/2] net/ethtool: Add new coalescing parameter for queue

On Tue, 2015-12-08 at 10:02 -0800, Shannon Nelson wrote:
> On Mon, Dec 7, 2015 at 8:42 PM,  <kan.liang@...el.com> wrote:
> > From: Kan Liang <kan.liang@...el.com>
> > 
> > Intrdouce "queue" option for coalesce getting and setting.
[...]
> > --- a/net/core/ethtool.c
> > +++ b/net/core/ethtool.c
> > @@ -1123,10 +1123,16 @@ static noinline_for_stack int ethtool_get_coalesce(struct net_device *dev,
> >                                                    void __user *useraddr)
> >  {
> >         struct ethtool_coalesce coalesce = { .cmd = ETHTOOL_GCOALESCE };
> > +       struct ethtool_coalesce tmp = { .queue = -1 };
> > 
> >         if (!dev->ethtool_ops->get_coalesce)
> >                 return -EOPNOTSUPP;
> > 
> > +       if (copy_from_user(&tmp, useraddr, sizeof(coalesce)))
> > +               return -EFAULT;
> > +
> > +       coalesce.queue = tmp.queue;
> > +
> 
> Is this going to do what you expect when you have an older ethtool
> program?  It seems to me that the older ethtool program will have the
> original coalesce struct without the new queue field, so when you do
[...]

Indeed, it's not safe to extend UAPI structures like this.

Ben.

-- 
Ben Hutchings
Life would be so much easier if we could look at the source code.
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