netdev - Re: [iproute2-next v2 4/4] vdpa: Enable user to set mtu of the vdpa device

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Message-ID: <20211218170602-mutt-send-email-mst@kernel.org>
Date:   Sat, 18 Dec 2021 17:07:15 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Parav Pandit <parav@...dia.com>, stephen@...workplumber.org,
        netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        jasowang@...hat.com
Subject: Re: [iproute2-next v2 4/4] vdpa: Enable user to set mtu of the vdpa
 device

On Sat, Dec 18, 2021 at 01:53:01PM -0700, David Ahern wrote:
> On 12/17/21 1:08 AM, Parav Pandit wrote:
> > @@ -204,6 +217,8 @@ static void vdpa_opts_put(struct nlmsghdr *nlh, struct vdpa *vdpa)
> >  	if (opts->present & VDPA_OPT_VDEV_MAC)
> >  		mnl_attr_put(nlh, VDPA_ATTR_DEV_NET_CFG_MACADDR,
> >  			     sizeof(opts->mac), opts->mac);
> > +	if (opts->present & VDPA_OPT_VDEV_MTU)
> > +		mnl_attr_put_u16(nlh, VDPA_ATTR_DEV_NET_CFG_MTU, opts->mtu);
> 
> Why limit the MTU to a u16? Eric for example is working on "Big TCP"
> where IPv6 can work with Jumbograms where mtu can be > 64k.
> 
> https://datatracker.ietf.org/doc/html/rfc2675

Well it's 16 bit at the virtio level, though we can extend that of
course. Making it match for now removes need for validation.
-- 
MST