Re: [Qemu-devel] Help for beginner

[Ady Wahyudi Paundu <awpaundu@gmail.com>]

Hi again, I am sorry for multiple reply, but i forget to mention one
other thing.

I also use lttng-ust method, and like my printf() attempt, I put my
new defined trace points into all function within net/net.c, net/tap.c
and hw/net/virtio-net.c.  Using this approach, i also cannot capture
my new trace points when doing 'ping'.  I am sure that i added my new
trace points correctly because i can list them using 'lttng list -u'

what did i do wrong?

~Ady

On 1/26/15, Ady Wahyudi Paundu <awpaundu@gmail.com> wrote:
> Hi Stefan, thank you for the tips.
>
> I was trying the way you suggested to add printfs.
> For starter I try to put them into all function within net/net.c,
> net/tap.c and hw/net/virtio-net.c (I run qemu using virtio netcard).
> However, there were no printf message showed up (when i started a qemu
> process and when i tried ping from within the guest OS of that qemu
> process). As if those functions were not used.
> Do you think I put those trace points in a wrong functions?
>
> Thanks in advance
> ~Ady
>
> On 1/16/15, Stefan Hajnoczi <stefanha@gmail.com> wrote:
>
>>
>> Assuming you run qemu-system-x86_64 the default network card is an
>> emulated Intel e1000 NIC.
>>
>> See hw/net/e1000.c:start_xmit() for the function that emulates packet
>> transmission.  It loops over the transmit descriptor ring and send off
>> each packet that the guest has enqueued using qemu_send_packet().
>>
>> qemu_send_packet() is a QEMU network subsystem API that passes the
>> packet to a host network device (for example, -netdev tap).  What
>> happens next depends on which netdev the user launched QEMU with (the
>> default is 'user').
>>
>> The most popular netdev in production is tap.  Look at
>> net/tap.c:tap_receive() to see how QEMU writes the guest's packet to the
>> tap device on the host.
>>
>> The tap driver in the host kernel will then "receive" the packet from
>> the guest and process it further (often the user has configured a
>> software bridge device so the packet will be forwarded onto the host's
>> physical NIC).
>>
>> Just to recap the structure is:
>>
>>  guest <-> emulated e1000 NIC <-> tap netdev <-> host kernel
>>
>> Use tcpdump in the guest or host, or add printfs to QEMU if you want to
>> follow traffic further.
>>
>> Good luck,
>> Stefan
>>
>