From: Stephen Hemminger <stephen@networkplumber.org>
To: Aaron Conole <aconole@redhat.com>
Cc: netdev@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org,
"Michael S. Tsirkin" <mst@redhat.com>
Subject: Re: [RFC v2 -next 1/2] virtio: Start feature MTU support
Date: Thu, 17 Mar 2016 15:04:59 -0700 [thread overview]
Message-ID: <20160317150459.49bf5c9b@samsung9> (raw)
In-Reply-To: <f7tfuvox128.fsf@redhat.com>
On Thu, 17 Mar 2016 17:10:55 -0400
Aaron Conole <aconole@redhat.com> wrote:
> Stephen Hemminger <stephen@networkplumber.org> writes:
>
> > On Tue, 15 Mar 2016 17:04:12 -0400
> > Aaron Conole <aconole@redhat.com> wrote:
> >
> >> --- a/include/uapi/linux/virtio_net.h
> >> +++ b/include/uapi/linux/virtio_net.h
> >> @@ -55,6 +55,7 @@
> >> #define VIRTIO_NET_F_MQ 22 /* Device supports Receive Flow
> >> * Steering */
> >> #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */
> >> +#define VIRTIO_NET_F_MTU 25 /* Device supports Default MTU Negotiation */
> >>
> >> #ifndef VIRTIO_NET_NO_LEGACY
> >> #define VIRTIO_NET_F_GSO 6 /* Host handles pkts w/ any GSO type */
> >> @@ -73,6 +74,8 @@ struct virtio_net_config {
> >> * Legal values are between 1 and 0x8000
> >> */
> >> __u16 max_virtqueue_pairs;
> >> + /* Default maximum transmit unit advice */
> >> + __u16 mtu;
> >> } __attribute__((packed));
> >>
> >> /*
> >
> > You can't change user visible headers without breaking ABI.
> > This structure might be used by other user code. Also how can this
> > work if host is using old size of structure.
>
> How else can this field be added and remain compliant with the spec? The
> spec requires that mtu be passed in the virtio_net_config field.
>
> As for old sizeof, I think the absence of the VIRTIO_NET_F_MTU bit being
> asserted is confirmation that mtu is not valid (at least, it is implied
> in the spec).
Michael is right as long as the code checks for MTU flag before
referencing the mtu field, everything is fine. Actually, the structure
is never used directly only by fetching fields with offsetof
next prev parent reply other threads:[~2016-03-17 22:04 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-15 21:04 [RFC v2 -next 0/2] virtio-net: Advised MTU feature Aaron Conole
2016-03-15 21:04 ` [RFC v2 -next 1/2] virtio: Start feature MTU support Aaron Conole
2016-03-16 18:23 ` Stephen Hemminger
2016-03-16 18:29 ` Michael S. Tsirkin
2016-03-17 21:10 ` Aaron Conole
2016-03-17 22:04 ` Stephen Hemminger [this message]
2016-03-15 21:04 ` [RFC v2 -next 2/2] virtio_net: Read the advised MTU Aaron Conole
2016-03-16 14:11 ` Sergei Shtylyov
2016-03-17 21:15 ` Aaron Conole
2016-03-16 14:24 ` Michael S. Tsirkin
2016-03-17 21:20 ` Aaron Conole
2016-03-15 21:34 ` [RFC v2 -next 0/2] virtio-net: Advised MTU feature Rick Jones
2016-03-17 21:24 ` Aaron Conole
2016-03-16 4:55 ` Pankaj Gupta
2016-03-17 21:24 ` Aaron Conole
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160317150459.49bf5c9b@samsung9 \
--to=stephen@networkplumber.org \
--cc=aconole@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mst@redhat.com \
--cc=netdev@vger.kernel.org \
--cc=virtualization@lists.linux-foundation.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).