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Re: [Qemu-devel] [PATCH net-next v2 1/3] virtio_net: propagate linkspeed
From: |
Jason Baron |
Subject: |
Re: [Qemu-devel] [PATCH net-next v2 1/3] virtio_net: propagate linkspeed/duplex settings from the hypervisor |
Date: |
Thu, 28 Dec 2017 10:53:54 -0500 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 |
On 12/27/2017 04:43 PM, David Miller wrote:
> From: Jason Baron <address@hidden>
> Date: Fri, 22 Dec 2017 16:54:01 -0500
>
>> The ability to set speed and duplex for virtio_net in useful in various
>> scenarios as described here:
>>
>> 16032be virtio_net: add ethtool support for set and get of settings
>>
>> However, it would be nice to be able to set this from the hypervisor,
>> such that virtio_net doesn't require custom guest ethtool commands.
>>
>> Introduce a new feature flag, VIRTIO_NET_F_SPEED_DUPLEX, which allows
>> the hypervisor to export a linkspeed and duplex setting. The user can
>> subsequently overwrite it later if desired via: 'ethtool -s'.
>>
>> Signed-off-by: Jason Baron <address@hidden>
>> Cc: "Michael S. Tsirkin" <address@hidden>
>> Cc: Jason Wang <address@hidden>
>
> Looks mostly fine to me but need some virtio_net reviewers on this one.
>
>> @@ -57,6 +57,8 @@
>> * Steering */
>> #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */
>>
>> +#define VIRTIO_NET_F_SPEED_DUPLEX 63 /* Host set linkspeed and
>> duplex */
>> +
>
> Why use a value so far away from the largest existing one?
>
> Just curious.
>
So that came from a discussion with Michael about which bit to use for
this, and he suggested using 63:
"
Transports started from bit 24 and are growing up.
So I would say devices should start from bit 63 and grow down.
"
https://patchwork.ozlabs.org/patch/848814/#1826669
I will add a comment to explain it.
Thanks,
-Jason