On 2018/11/15 12:19, Jason Wang wrote:
>
> On 2018/11/15 上午11:56, jiangyiwen wrote:
>> Hi Stefan, Michael, Jason and everyone,
>>
>> Several days ago, I discussed with jason about "Vsock over Virtio-net".
>> This idea has two advantages:
>> First, it can use many great features of virtio-net, like batching,
>> mergeable rx buffer and multiqueue, etc.
>> Second, it can reduce many duplicate codes and make it easy to be
>> maintained.
>>
>> Before the implement, I want to discuss with everyone again, and
>> want to know everyone's suggestions.
>>
>> After the discussion, based on this point I will try to implement
>> this idea, but I am not familiar with the virtio-net, that is a
>> pity. :(
>
>
> I think we should have a new feature flag for this. E.g VIRTIO_NET_F_VSOCK.
> And host should fail the negotiation if guest doesn't support this to avoid
> confusion. When this feature is negotiated, we will use it only for VOSCK
> transport. This can simplify things somehow.
>
>
>> -------------------------Simple idea------------------------------
>>
>> 1. The packet layout will become as follows:
>>
>> +---------------------------------+
>> | Virtio-net header |
>> |(struct virtio_net_hdr_mrg_rxbuf)|
>> +---------------------------------+
>> | Vsock header |
>> | (struct virtio_vsock_hdr) |
>> +---------------------------------+
>> | payload |
>> | (until end of packet) |
>> +---------------------------------+
>>
>> 2. The Guest->Host basic code flow as follow:
>> +------------+
>> | Client |
>> +------------+
>> |
>> |
>> +------------------------------------------------------------------+
>> |VSOCK Core Module |
>> |ops->sendmsg; (vsock_stream_sendmsg) |
>> | -> alloc_skb; /* it will packet a skb buffer, and include vsock |
>> | * hdr and payload */ |
>> | -> dev_queue_xmit(); /* it will call start_xmit(virtio-net.c) */|
>> |vsock hdr and payload, and then call |
>> +------------------------------------------------------------------+
>
>
> Note, if we've negotiated the feature, virtio-net driver must not use
> register_netdev to register it to network core. This can avoid lots of
> confusion.
Hi Jason,
You mean we should not register netdev if use vsock, and in order to
avoid confusion, then I think whether we should keep vsock and export
some virtio-net's functions that can be shared. In this way, first, vsock
may keep existing architecture and will not affect virtio-net. In addition,
vsock doesn't need to use virtio_net header too, then it don't need to pack
skb structure.
Thanks,
Yiwen.
>
>
>> |
>> |
>> +------------------------------------------------------------------+
>> |Virtio-net Module |
>> |start_xmit |
>> | -> add virtio_net_hdr and pack sg in ring desc, notify Host |
>> +------------------------------------------------------------------+
>> |
>> |
>> +------------------------------------------------------------------+
>> |Vhost-net Module |
>> |handle_tx |
>> | -> get tx buffer, skip virtio_net_hdr and call Vsock function. |
>> | /* This point has some differences, vhost-net use ->sendmsg to |
>> | * forward information, however vsock only need to notify server |
>> | * that data ready. */ |
>> +------------------------------------------------------------------+
>
>
> When VIRTIO_NET_F_VOSCK is negotiated, we know that it's a vsock transport,
> we can then forward it to vsock core.
>
>
>> |
>> |
>> +------------------------------------------------------------------+
>> |VSOCK Core Module |
>> |alloc_pkt, copy skb data to pkt. |
>> |add pkt to rx_queue and notify server to get data. |
>> +------------------------------------------------------------------+
>>
>> 3. To Host->Guest
>> I have a problem and difficult, mainly I know about virtio-net a little),
>> because I have been doing work related with storage and file system.
>>
>> The problem as follows:
>> we should monitor all of socket of vsock in handle_rx, when there are
>> data coming, and copy data to vq desc. Vhost-net use ->recvmsg to
>> get data, it is different with socket. To vsock, I think host will
>> not call ->recvmsg when it need to send message to guest. To net,
>> vhost-net only as forwarding layer.
>
> Know not much here, but is it possible to have a vsock(tap) to be passed to
> vhost_net and let vhost call its recvmgs()? Bascially it was a socket on host
> as well I believe?
For vsock, Host->Guest, it's code flow as follows:
Server call send()
-> sendmsg(); (vsock_stream_sendmsg)
-> virtio_trasnport_send_pkt_info
-> alloc pkt, add pkt to send_pkt_list, wake up vhost_worker
Vhost_worker
-> vhost_transport_send_pkt_work
-> get pkt from send_pkt_list
-> get vq input desc and then fill data to desc addr
-> update used ring and then signal guest
In the whole process, host don't call recvmsg() because it is a net device, and
it also receives any messages.
For vhost-net, I understand it is a tap device, so it can receive messages
from other net device.
This is my understanding, it may have some errors.
Thanks.
>
> If this doesn't work, we can have vsock specific receiving routine in
> vhost_net if VIRTIO_NET_F_VOSCK is negotiated.
>
> Generally, I think we should try out best to keep the exist
> sendmsg()/recvmsg() interfaces and only consider the alternatives if we meet
> some real blocker.
>
> Thanks
>
>
>>
>
> .
>
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