Using Qemu for BMC with a TAP interface

[Cédric Le Goater]

On 12/1/21 16:59, Peter Foley wrote:
> The container system we're using (https://research.google/pubs/pub43438 <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.

ok. That's interesting. You are running QEMU BMC machines (Nuvotons and Aspeed ?)
wrapped in containers. Why BMC machines?

I guess we could reproduce the setup with a single instance to check issues but
it's a lot of work for an uncommon scenario.

Thanks,

C.


> 
> On Tue, Nov 30, 2021 at 7:54 PM Patrick Venture <venture at google.com <mailto:venture at google.com>> wrote:
> 
> 
> 
>     On Mon, Nov 22, 2021 at 12:14 AM Cédric Le Goater <clg at kaod.org <mailto: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 <mailto: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
>