Using Qemu for BMC with a TAP interface

[Patrick Venture]

On Wed, Dec 1, 2021 at 12:44 PM Patrick Venture <venture at google.com> wrote:

>
>
> On Wed, Dec 1, 2021 at 9:08 AM Cédric Le Goater <clg at kaod.org> wrote:
>
>> 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?
>>
>
> We're running BMC machines to validate BMC firmware.
>
>
>>
>> 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.
>>
>
https://lists.gnu.org/archive/html/qemu-devel/2021-12/msg00450.html - turns
out at least this was a bug preventing packets from being received.  The
tap fd wasn't being reactivated in all cases.


>
>> 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
>> >
>>
>>
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