Using Qemu for BMC with a TAP interface

[Joel Stanley]

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.

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

I've cc'd Cédric as he is the king of qemu command lines.

Cheers,

Joel






>
> Patrick