Using Qemu for BMC with a TAP interface

[Peter Foley]

The container system we're using (https://research.google/pubs/pub43438)
provides a set of FDs connected to a pre-configured TAP device, so I don't
think manual bridge configuration is an option.

On Tue, Nov 30, 2021 at 7:54 PM Patrick Venture <venture at google.com> wrote:

>
>
> On Mon, Nov 22, 2021 at 12:14 AM Cédric Le Goater <clg at kaod.org> wrote:
>
>> Hello,
>>
>> On 11/22/21 08:20, Joel Stanley wrote:
>> > On Thu, 18 Nov 2021 at 20:35, Patrick Venture <venture at google.com>
>> wrote:
>> >>
>> >> Hi;
>> >>
>> >> We're working on wiring up our Qemu BMC via a TAP configuration, and
>> we're not seeing packets inside the Nuvoton NIC itself (a level of
>> debugging we had to enable).  We're using the npcm7xx SoC device,
>> >>
>> >> -nic
>> tap,fds=4:5:6:7:8:9:10:11,id=net0,model=npcm7xx-emc,mac=58:cb:52:18:b8:f7
>> >>
>> >> For the networking parameters, where the tap fds are valid.  I was
>> curious if any of y'all got qemu networking working for your BMC SoCs,
>> either Aspeed or Nuvoton?
>> >
>> > I've not tried using the -nic tap option with file descriptors. It's
>> > not quite clear what you're trying to do, or what your full setup
>> > looks like.
>>
>> yes. could you explain please ? It is simpler to run with a netdev bridge
>> backend :
>>
>>    -net nic,macaddr=C0:FF:EE:00:00:03,netdev=net0 -netdev
>> bridge,id=net0,helper=/usr/libexec/qemu-bridge-helper,br=virbr0
>>
>
> Thanks for the replies and help.  I don't know why my mail didn't decide
> this should go in my inbox.  Probably user error on my part in the filters.
>
> Peter, would a network bridge simplify life?  I imagine the file
> descriptor approach is because of the framework configuring Qemu, but
> wanted to ask.
>
>>
>>
>> Thanks,
>>
>> C.
>>
>> >
>> > I did test it out just now with a manually created tap interface:
>> >
>> > sudo ip tuntap add test0 mode tap group netdev
>> > sudo ip link set test0 up
>> > sudo tcpdump -i test0
>> >
>> > And then when I fired up a qemu instance,
>> >
>> > qemu-system-arm -nographic -M romulus-bmc -kernel arch/arm/boot/zImage
>> > -dtb arch/arm/boot/dts/aspeed-bmc-opp-romulus.dtb -initrd arm.cpio.xz
>> > -nic tap,ifname=test0,id=net0
>> >
>> > I could see packets being decoded by the tcpdump instance (my laptop
>> > is 'voyager', qemu came up as fe80::5054:ff:fe12:3456):
>> >
>> > $ sudo tcpdump -i test0
>> > tcpdump: verbose output suppressed, use -v[v]... for full protocol
>> decode
>> > listening on test0, link-type EN10MB (Ethernet), snapshot length 262144
>> bytes
>> > 15:10:32.683930 IP6 voyager > ip6-allrouters: ICMP6, router
>> > solicitation, length 16
>> > 15:10:33.655994 IP6 voyager.mdns > ff02::fb.mdns: 0 [2q] PTR (QM)?
>> > _ipps._tcp.local. PTR (QM)? _ipp._tcp.local. (45)
>> > 15:10:37.795242 IP6 fe80::5054:ff:fe12:3456 > ip6-allrouters: ICMP6,
>> > router solicitation, length 16
>> > 15:11:05.688413 IP6 voyager.mdns > ff02::fb.mdns: 0 [2q] PTR (QM)?
>> > _ipps._tcp.local. PTR (QM)? _ipp._tcp.local. (45)
>> > 15:11:07.499841 IP6 voyager > ip6-allrouters: ICMP6, router
>> > solicitation, length 16
>> > 15:11:11.079030 IP6 fe80::5054:ff:fe12:3456 > ip6-allrouters: ICMP6,
>> > router solicitation, length 16
>>
>
> Thanks, so with the ftgmac100 nic, you're able to talk to qemu via tap.  I
> didn't see any obvious differences in the npcm7xx_emc device.
>
>
>> >
>> > I've cc'd Cédric as he is the king of qemu command lines.
>> >
>> > Cheers,
>> >
>> > Joel
>> >
>> >
>> >
>> >
>> >
>> >
>> >>
>> >> Patrick
>>
>>
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