Re: [RFC] virtio: enforce link up

[Vincent Jardin]

On 10/15/23 10:42, Michael S. Tsirkin wrote:
> On Sat, Oct 14, 2023 at 09:06:09PM +0000, Vincent Jardin wrote:
>> On 10/14/23 18:37, Michael S. Tsirkin wrote:
>>> On Sat, Oct 14, 2023 at 06:22:34PM +0200, Vincent Jardin wrote:
>>>> Using interface's settings, let's enforce an always on link up.
>>>>
>>>> Signed-off-by: Vincent Jardin <vincent.jardin@ekinops.com>
>>>
>>> What is going on here? Just don't set it down.
>>
>> The purpose is to have a stable vLink for the VMs that don't support
>> such sysctl arp_evict_nocarrier:
>> https://patchwork.kernel.org/project/netdevbpf/patch/20211101173630.300969-2-prestwoj@gmail.com/
>>
>> We are facing some users of vSwitches that use vhost-user and that
>> disconnect and reconnect during some operations. For most of the VMs on
>> their deployments with such vSwitches, those VMs' vLink should not flap.
>>
>> For those VMs, the flaps are critical and they can lead to some
>> convergence issues.
>>
>> If this capability is not at the virtio-net level, should it be at
>> qemu's net_vhost_user_event() ?
>> For instance, from
>> https://github.com/qemu/qemu/blob/63011373ad22c794a013da69663c03f1297a5c56/net/vhost-user.c#L266
>> ?
>>
>> best regards,
>>     Vincent
> 
> 
> makes sense

OK, I've just submitted a RFC draft v2 assuming net/vhost-user.c instead 
of net-virtio.



> 
>>
>>>
>>>> ---
>>>>    hw/net/virtio-net.c            | 8 ++++++++
>>>>    include/hw/virtio/virtio-net.h | 2 ++
>>>>    2 files changed, 10 insertions(+)
>>>>
>>>> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
>>>> index 29e33ea5ed..e731b4fdea 100644
>>>> --- a/hw/net/virtio-net.c
>>>> +++ b/hw/net/virtio-net.c
>>>> @@ -78,6 +78,9 @@
>>>>       tso/gso/gro 'off'. */
>>>>    #define VIRTIO_NET_RSC_DEFAULT_INTERVAL 300000
>>>>    
>>>> +/* force always link up */
>>>> +#define VIRTIO_NET_LINK_UP false
>>>> +
>>>>    #define VIRTIO_NET_RSS_SUPPORTED_HASHES (VIRTIO_NET_RSS_HASH_TYPE_IPv4 
>>>> | \
>>>>                                             VIRTIO_NET_RSS_HASH_TYPE_TCPv4 
>>>> | \
>>>>                                             VIRTIO_NET_RSS_HASH_TYPE_UDPv4 
>>>> | \
>>>> @@ -447,6 +450,9 @@ static void virtio_net_set_link_status(NetClientState 
>>>> *nc)
>>>>        else
>>>>            n->status |= VIRTIO_NET_S_LINK_UP;
>>>>    
>>>> +    if (n->net_conf.link_up)
>>>> +        n->status |= VIRTIO_NET_S_LINK_UP;
>>>> +
>>>>        if (n->status != old_status)
>>>>            virtio_notify_config(vdev);
>>>>    
>>>> @@ -3947,6 +3953,8 @@ static Property virtio_net_properties[] = {
>>>>                          VIRTIO_NET_F_GUEST_USO6, true),
>>>>        DEFINE_PROP_BIT64("host_uso", VirtIONet, host_features,
>>>>                          VIRTIO_NET_F_HOST_USO, true),
>>>> +    DEFINE_PROP_BOOL("link_up", VirtIONet, net_conf.link_up,
>>>> +                       VIRTIO_NET_LINK_UP),
>>>>        DEFINE_PROP_END_OF_LIST(),
>>>>    };
>>>>    
>>>> diff --git a/include/hw/virtio/virtio-net.h 
>>>> b/include/hw/virtio/virtio-net.h
>>>> index 55977f01f0..385bebab34 100644
>>>> --- a/include/hw/virtio/virtio-net.h
>>>> +++ b/include/hw/virtio/virtio-net.h
>>>> @@ -56,6 +56,7 @@ typedef struct virtio_net_conf
>>>>        char *duplex_str;
>>>>        uint8_t duplex;
>>>>        char *primary_id_str;
>>>> +    bool link_up; /* if set enforce link up, never down */
>>>>    } virtio_net_conf;
>>>>    
>>>>    /* Coalesced packets type & status */
>>>> @@ -180,6 +181,7 @@ struct VirtIONet {
>>>>        size_t guest_hdr_len;
>>>>        uint64_t host_features;
>>>>        uint32_t rsc_timeout;
>>>> +    uint32_t link_up; /* if set enforce link up, never down */
>>>>        uint8_t rsc4_enabled;
>>>>        uint8_t rsc6_enabled;
>>>>        uint8_t has_ufo;
>>>> -- 
>>>> 2.34.1
>>>
>>
>