From: "Michael S. Tsirkin" <mst@redhat.com>
To: Parav Pandit <parav@nvidia.com>
Cc: "stephen@networkplumber.org" <stephen@networkplumber.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"virtualization@lists.linux-foundation.org"
<virtualization@lists.linux-foundation.org>,
David Ahern <dsahern@gmail.com>
Subject: Re: [iproute2-next v2 4/4] vdpa: Enable user to set mtu of the vdpa device
Date: Mon, 20 Dec 2021 07:02:58 -0500 [thread overview]
Message-ID: <20211220070136-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <PH0PR12MB548189EBA8346A960A0A409FDC7B9@PH0PR12MB5481.namprd12.prod.outlook.com>
On Mon, Dec 20, 2021 at 03:49:21AM +0000, Parav Pandit wrote:
>
>
> > From: Michael S. Tsirkin <mst@redhat.com>
> > Sent: Sunday, December 19, 2021 3:37 AM
> >
> > 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.
> > --
> As Michael mentioned virtio specification limits the mtu to 64k-1. Hence 16-bit.
> First we need to update the virtio spec to support > 64K mtu.
> However, when/if (I don't know when) that happens, we need to make this also u32.
> So may be we can make it u32 now, but still restrict the mtu value to 64k-1 in kernel, until the spec is updated.
>
> Let me know, if you think that's future proofing is better, I first need to update the kernel to take nla u32.
>
> > MST
After consideration, this future proofing seems like a good thing to have.
--
MST
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next prev parent reply other threads:[~2021-12-20 12:03 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-17 8:08 [iproute2-next v2 0/4] vdpa tool to query and set config layout Parav Pandit via Virtualization
2021-12-17 8:08 ` [iproute2-next v2 1/4] vdpa: Update kernel headers Parav Pandit via Virtualization
2021-12-17 8:08 ` [iproute2-next v2 2/4] vdpa: Enable user to query vdpa device config layout Parav Pandit via Virtualization
2021-12-17 8:08 ` [iproute2-next v2 3/4] vdpa: Enable user to set mac address of vdpa device Parav Pandit via Virtualization
2021-12-17 8:08 ` [iproute2-next v2 4/4] vdpa: Enable user to set mtu of the " Parav Pandit via Virtualization
2021-12-18 20:53 ` David Ahern
2021-12-18 22:07 ` Michael S. Tsirkin
2021-12-20 3:49 ` Parav Pandit via Virtualization
2021-12-20 12:02 ` Michael S. Tsirkin [this message]
2021-12-20 19:11 ` Parav Pandit via Virtualization
2021-12-20 21:11 ` David Ahern
2021-12-20 23:06 ` Michael S. Tsirkin
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