"Michael S. Tsirkin" <mst@xxxxxxxxxx> writes:
> On Thu, Oct 20, 2016 at 10:37:20PM -0400, Jarod Wilson wrote:
>> On Thu, Oct 20, 2016 at 11:23:54PM +0300, Michael S. Tsirkin wrote:
>> > On Thu, Oct 20, 2016 at 01:55:21PM -0400, Jarod Wilson wrote:
>> ...
>> > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> > > index fad84f3..720809f 100644
>> > > --- a/drivers/net/virtio_net.c
>> > > +++ b/drivers/net/virtio_net.c
>> > > @@ -1419,17 +1419,6 @@ static const struct ethtool_ops virtnet_ethtool_ops = {
>> > > .set_settings = virtnet_set_settings,
>> > > };
>> > >
>> > > -#define MIN_MTU 68
>> > > -#define MAX_MTU 65535
>> > > -
>> > > -static int virtnet_change_mtu(struct net_device *dev, int new_mtu)
>> > > -{
>> > > - if (new_mtu < MIN_MTU || new_mtu > MAX_MTU)
>> > > - return -EINVAL;
>> > > - dev->mtu = new_mtu;
>> > > - return 0;
>> > > -}
>> > > -
>> > > static const struct net_device_ops virtnet_netdev = {
>> > > .ndo_open = virtnet_open,
>> > > .ndo_stop = virtnet_close,
>> > > @@ -1437,7 +1426,6 @@ static const struct net_device_ops virtnet_netdev = {
>> > > .ndo_validate_addr = eth_validate_addr,
>> > > .ndo_set_mac_address = virtnet_set_mac_address,
>> > > .ndo_set_rx_mode = virtnet_set_rx_mode,
>> > > - .ndo_change_mtu = virtnet_change_mtu,
>> > > .ndo_get_stats64 = virtnet_stats,
>> > > .ndo_vlan_rx_add_vid = virtnet_vlan_rx_add_vid,
>> > > .ndo_vlan_rx_kill_vid = virtnet_vlan_rx_kill_vid,
>> > > @@ -1748,6 +1736,9 @@ static bool virtnet_validate_features(struct virtio_device *vdev)
>> > > return true;
>> > > }
>> > >
>> > > +#define MIN_MTU ETH_MIN_MTU
>> > > +#define MAX_MTU ETH_MAX_MTU
>> > > +
>> >
>> > Can we drop these btw?
>>
>> Bah. Yeah. Should have just used them directly. I didn't add ETH_MAX_MTU
>> until after doing the virtio_net changes, so I missed that.
>>
>> > > static int virtnet_probe(struct virtio_device *vdev)
>> > > {
>> > > int i, err;
>> > > @@ -1821,6 +1812,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>> > >
>> > > dev->vlan_features = dev->features;
>> > >
>> > > + /* MTU range: 68 - 65535 */
>> > > + dev->min_mtu = MIN_MTU;
>> > > + dev->max_mtu = MAX_MTU;
>> > > +
>> > > /* Configuration may specify what MAC to use. Otherwise random. */
>> > > if (virtio_has_feature(vdev, VIRTIO_NET_F_MAC))
>> > > virtio_cread_bytes(vdev,
>> > > @@ -1875,8 +1870,10 @@ static int virtnet_probe(struct virtio_device *vdev)
>> > > mtu = virtio_cread16(vdev,
>> > > offsetof(struct virtio_net_config,
>> > > mtu));
>> > > - if (virtnet_change_mtu(dev, mtu))
>> > > + if (mtu < dev->min_mtu || mtu > dev->max_mtu)
>> >
>> > In fact the > max_mtu branch does not make sense since a 16 bit
>> > value can't exceed MAX_MTU.
>>
>> Hm. mtu is declared as an int, not sure if there's any sort of type
>> promotion to be worried about (not an area I know much/anything about).
>
> Not by design, that's for sure.
If you're really worried, we could declare it as a u16. The value
returned from virtio_cread16 is type u16, and there are no type
promotion rules I'm aware of that would do the wrong thing there.
>> Certainly something that could be looked into as a minor optimization,
>> though it's only in a probe path and shouldn't hurt anything, so ... meh?
>
> Right. Aaron said he's working on a patch that essentially does
> dev->max_mtu = mtu after validation, so this part will look
> a bit silly there.
Agreed, but I can do that in my patch if you don't want the extra churn.
-Aaron
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