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Re: [Qemu-devel] tap networking - how?
From: |
Alexey Kardashevskiy |
Subject: |
Re: [Qemu-devel] tap networking - how? |
Date: |
Thu, 13 Feb 2014 21:34:49 +1100 |
User-agent: |
Mozilla/5.0 (X11; Linux i686 on x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 |
On 02/13/2014 07:40 PM, Max Filippov wrote:
> Hi,
>
> On Thu, Feb 13, 2014 at 11:34 AM, Alexey Kardashevskiy <address@hidden> wrote:
>> Hi!
>>
>> I am debugging spapr-vlan and hit the following issue.
>>
>> When I run QEMU as below, the kernel's DHCP client does not continue till I
>> hit any key in console. If I replace spapr-vlan with
>> e1000/rtl8139/virtio-net, everything is just fine. If I use "user" network
>> - everything is fine too. So the problem is with combination of spapr-vlan
>> + tap.
>>
>> The issue looks like - the guest kernel boots and then prints:
>> Sending DHCP requests ..
>> and it keeps printing dots till I press key or timeout expires. tcpdump
>> (running on the tap interface) shows one DHCP request and one DHCP response.
>>
>> What normally happens is that QEMU calls os_host_main_loop_wait() which
>> calls qemu_poll_ns() and it is sitting there till eventfd signals.
>> This eventfd is registered via qemu_init_main_loop() -> aio_context_new()
>> -> aio_set_event_notifier() but I cannot find where it gets passed to the
>> kernel (otherwise why would we need eventfd?). When eventfd signals, QEMU
>> calls qemu_iohandler_poll() which checks if TAP device has something to
>> read and eventually calls tap_send().
>>
>> However in my bad example QEMU does not exit qemu_poll_ns() on eventfd,
>> only on stdin event.
>>
>> I can see AIO eventfd created and event_notifier_test_and_clear() is called
>> on it before the kernel starts using spapr-vlan.
>>
>> So. h_send_logical_lan() is called to sent a DHCP request packet. Now I
>> expect eventfd to signal but this does not happen. Have I missed some reset
>> or notification request or "bottom half" (virtio-net uses them but
>> e1000/rtl8139 do not)?
>
> Sounds pretty much like the problem I had recently with opencores
> 10/100 MAC:
> https://lists.gnu.org/archive/html/qemu-devel/2014-02/msg00073.html
>
> Does the following help?:
Yes, it does, thanks a lot!
While we are here and you seem to understand this stuff -
how is tap expected to work to deliver a packet from the external network
to the guest? I mean what event should be triggered in what order? My brain
is melting :( I just cannot see how receiving a packet on "tap" in the host
kernel can make os_host_main_loop_wait() exit in QEMU so it could call
qemu_iohandler_poll() and do the job. Thanks!
> diff --git a/hw/net/spapr_llan.c b/hw/net/spapr_llan.c
> index 1bd6f50..2436b5e 100644
> --- a/hw/net/spapr_llan.c
> +++ b/hw/net/spapr_llan.c
> @@ -404,6 +404,7 @@ static target_ulong
> h_add_logical_lan_buffer(PowerPCCPU *cpu,
> vio_stq(sdev, dev->buf_list + dev->add_buf_ptr, buf);
>
> dev->rx_bufs++;
> + qemu_flush_queued_packets(qemu_get_queue(dev->nic));
>
> DPRINTF("h_add_logical_lan_buffer(): Added buf ptr=%d rx_bufs=%d"
> " bd=0x%016llx\n", dev->add_buf_ptr, dev->rx_bufs,
>
>
--
Alexey
- [Qemu-devel] tap networking - how?, Alexey Kardashevskiy, 2014/02/13
- Re: [Qemu-devel] tap networking - how?, Max Filippov, 2014/02/13
- Re: [Qemu-devel] tap networking - how?,
Alexey Kardashevskiy <=
- Re: [Qemu-devel] tap networking - how?, Max Filippov, 2014/02/13
- Re: [Qemu-devel] tap networking - how?, Alexey Kardashevskiy, 2014/02/13
- Re: [Qemu-devel] tap networking - how?, Max Filippov, 2014/02/13
- Re: [Qemu-devel] tap networking - how?, Alexey Kardashevskiy, 2014/02/13
- Re: [Qemu-devel] tap networking - how?, Max Filippov, 2014/02/13
- Re: [Qemu-devel] tap networking - how?, Alexey Kardashevskiy, 2014/02/13