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Re: [Qemu-devel] [PATCH V6 02/10] net/filter-mirror.c: Make filter mirro


From: Zhang Chen
Subject: Re: [Qemu-devel] [PATCH V6 02/10] net/filter-mirror.c: Make filter mirror support vnet support.
Date: Fri, 16 Jun 2017 16:36:38 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1



On 06/16/2017 10:17 AM, Jason Wang wrote:


On 2017年06月15日 16:10, Zhang Chen wrote:


On 06/15/2017 12:31 PM, Jason Wang wrote:


On 2017年06月14日 16:04, Zhang Chen wrote:


On 06/13/2017 05:14 PM, Jason Wang wrote:


On 2017年06月12日 17:27, Zhang Chen wrote:

+        if (nf->direction == NET_FILTER_DIRECTION_RX ||
+            nf->direction == NET_FILTER_DIRECTION_ALL) {
+            vnet_hdr_len = nf->netdev->vnet_hdr_len;

This can only work if e.g virtio-net set its own vnet_hdr_len. But looks like it use guest_hdr_len instead.

I see in hw/net/virtio-net.c use the "qemu_set_vnet_hdr_len(nc->peer, n->guest_hdr_len);" to set the nf->netdev->vnet_hdr_len, any case not include here?

You mean:

        if (peer_has_vnet_hdr(n) &&
            qemu_has_vnet_hdr_len(nc->peer, n->guest_hdr_len)) {
            qemu_set_vnet_hdr_len(nc->peer, n->guest_hdr_len);
            n->host_hdr_len = n->guest_hdr_len;
        }

?

From the code, it only set peer's vnet header when peer supports vnet_hdr up to n->guest_hdr_len. If peer can't, virtio-net will strip the header.

So, We should get the n->guest_hdr_len in another way? like set a new parameter in NetClientState?
Any suggestion about it?

Thanks
Zhang Chen

Rethink about this, a question is do we really care guest vnet header len? During guest transmission, when packet reaches netfilter. The vnet_header should have been stripped to netdev->vnet_hdr_len.

But we use filter-redirector send packet to colo-compare that get the packet with the vnet header.

That is colo-compare see:

address@hidden:colo_compare_pkt_info_src src/dst: 192.168.4.144 s: seq/ack=2181260317/2075177759 res=0 flags=18 spkt_size: 95

address@hidden:colo_compare_pkt_info_dst src/dst: 192.168.4.88 d: seq/ack=2181260317/2075177759 res=0 flags=18 dpkt_size: 95

colo-compare ppkt: 0000: 01 00 00 00 00 00 22 00 10 00 00 00 12 14 fc 1d ......"......... colo-compare ppkt: 0010: 1a 6b 52 54 00 12 34 56 08 00 45 00 00 45 12 61 .kRT..4V..E..E.a colo-compare ppkt: 0020: 40 00 40 06 9e 19 c0 a8 04 90 c0 a8 04 58 04 d2 @address@hidden colo-compare ppkt: 0030: ca 98 82 03 64 1d 7b b0 b3 1f 80 18 00 e3 8a 70 ....d.{........p colo-compare ppkt: 0040: 00 00 01 01 08 0a 00 00 5b fa 00 4d f1 aa 73 65 ........[..M..se colo-compare ppkt: 0050: 72 76 65 72 20 67 65 74 20 69 74 20 34 36 38 rver get it 468 colo-compare spkt: 0000: 01 00 00 00 00 00 22 00 10 00 00 00 12 14 fc 1d ......"......... colo-compare spkt: 0010: 1a 6b 52 54 00 12 34 56 08 00 45 00 00 45 12 61 .kRT..4V..E..E.a colo-compare spkt: 0020: 40 00 40 06 9e 19 c0 a8 04 90 c0 a8 04 58 04 d2 @address@hidden colo-compare spkt: 0030: ca 98 82 03 64 1d 7b b0 b3 1f 80 18 00 e3 8a 70 ....d.{........p colo-compare spkt: 0040: 00 00 01 01 08 0a 00 00 5c 02 00 4d f1 aa 73 65 ........\..M..se colo-compare spkt: 0050: 72 76 65 72 20 67 65 74 20 69 74 20 34 36 38 rver get it 468

So, colo-compare need to know the vnet_hdr_len for skip this field, then colo-compare
can parse the net packet correctly.
Back to this patch, how should I fix it?

Let me explain a little bit more. What I mean is that we should care only about the vnet header len of netdev instead of guest.

On RX direction (guest transmission). If you look at virtio_net_flush_tx(), before calling qemu_sendv_packet_async() where the packet can reach netfilers, virtio-net will copy only the parts that host is interested. So what we can see in e.g filter-mirror is netdev's vnet_hdr_len which is not guaranteed to be equal to guest hdr len.


If I understand correctly, should I copy the n->needs_vnet_hdr_swap flag to NetClientState ? Then, e.g filter-mirror can read the flag to decide the vnet_hdr_len value to send.


On TX direction, the packet will reach netfilter before it reaches virtio-net backend, so the vnet header is also netdev's vnet_hdr_len.

Does this explain?

Make sense.

Thanks
Zhang Chen



Thanks


Thanks
Zhang Chen



I still think use nf->netdev->vnet_hdr_len is sufficient.

Thanks



Thanks







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--
Thanks
Zhang Chen






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