[Xen-devel]How does xen-4.0.0 net backend work

[cc Luit <universalbillow@xxxxxxxxx>]

Hi, everyone.

These days I was reading the code of xen/linux/drivers/xen/netback/netback.c and xen/linux/drivers/net/xen-netfront.c 

in order to understand the control flow like how the domU transmit the packets from frontend to backend and then to the dom0 net-driver, but I came across some questions in netback.c.

    after the frontend transmitted the packets, dom0 schedule to the net_tx_tasklet, which goes to the net_tx_action() function:

1409 static void net_tx_action(unsigned long unused)

1410 {

1411         unsigned nr_mops;

1412         int ret;

1413

1414         if (dealloc_cons != dealloc_prod)

1415                 net_tx_action_dealloc();

1416

1417         nr_mops = net_tx_build_mops();

1418

1419         if (nr_mops == 0)

1420                 return;

1421

1422         ret = HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref,

1423                                         tx_map_ops, nr_mops);

1424         BUG_ON(ret);

1425

1426         net_tx_submit();

1427 }

in the net_tx_submit() function, it finally goes to a code:

1394                 netif_rx(skb);

so I'm curious why in the tx_submit there is a rx function? is the parameter skb the buffer that has been sent to the network? or it is the buffer that has not yet been sent? what is the netif_rx() function used to ?

Another question is: how the backend interact with the real dom0 driver? I cannot actually find the path    like what I speculate: backend push the packet to a buffer where linux driver will poll and send it to the real DMA ring...(it is just what I guess the interactive path is@@), can anyone explain the detail of it?

I'm not sure if I have expressed my questions clearly, it not, please tell me, I appreciate your help.

Thanks in advance:)

--
- Luit @ Parallel Processing Institute, Fudan University 

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