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

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Date:	Tue, 08 Dec 2015 19:45:44 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	"Liang, Kan" <kan.liang@...el.com>,
	"Nelson, Shannon" <shannon.nelson@...el.com>
Cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	"bwh@...nel.org" <bwh@...nel.org>,
	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"f.fainelli@...il.com" <f.fainelli@...il.com>,
	"alexander.duyck@...il.com" <alexander.duyck@...il.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"Wyborny, Carolyn" <carolyn.wyborny@...el.com>,
	"Skidmore, Donald C" <donald.c.skidmore@...el.com>,
	"Williams, Mitch A" <mitch.a.williams@...el.com>,
	"ogerlitz@...lanox.com" <ogerlitz@...lanox.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"jiri@...lanox.com" <jiri@...lanox.com>,
	"sfeldma@...il.com" <sfeldma@...il.com>,
	"gospo@...ulusnetworks.com" <gospo@...ulusnetworks.com>,
	"sasha.levin@...cle.com" <sasha.levin@...cle.com>,
	"dsahern@...il.com" <dsahern@...il.com>,
	"tj@...nel.org" <tj@...nel.org>,
	"cascardo@...hat.com" <cascardo@...hat.com>,
	"corbet@....net" <corbet@....net>
Subject: Re: [RFC 1/2] net/ethtool: Add new coalescing parameter for queue

On Tue, 2015-12-08 at 19:43 +0000, Liang, Kan wrote:
> 
> > 
> > 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.
> 
> Any suggestions for that?
> If we cannot extend the existing UAPI structures. I guess we have to add
> a new Ioctl like ETHTOOL_GCOALESCE_V2 for the new structure?

Something like that.

While you're at it, add a flags field which will indicate which of the
others are supported.  Also, there was some talk of adding settings for
RX DMA coalescing.

Ben.

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