Re: [PATCH] net/tap: add new macpair option for split MAC address

[Isaac Boukris <iboukris@gmail.com>]

Hi,

On Mon, Sep 30, 2024 at 12:55 AM Ferruh Yigit <ferruh.yigit@amd.com> wrote:
>
> On 9/17/2024 12:51 PM, Isaac Boukris wrote:
> > Normally, the MAC address of the kernel interface is the same as in the
> > interface in dpdk, as they represent the same interface. It is useful
> > to allow viewing them as separate connected interfaces (like ip's veth).
> >
> > This solves a problem I have running a freebsd-based IPv6 stack on top
> > of dpdk and using the tap interface, as both the kernel and freebsd
> > stacks configure the MAC derived IPv6 address on the interface (as can
> > be seen with ifconfig for the kernel), and they both complain about
> > duplicate IPv6 address and the freebsd disables IPv6 as a result.
> >
>
> How kernel side knows about the IPv6 address DPDK side uses, what is
> your tap usecase?

It derives it from the MAC address, which dpdk sets on it via ioclt,
to be the same as the dpdk interface.

As soon as dpdk is up, the interface has this IP configured:

ifconfig dpdk0
dpdk0: flags=4675<UP,BROADCAST,RUNNING,ALLMULTI,MULTICAST>  mtu 1500
        inet6 fe80::c830:cff:feda:9762  prefixlen 64  scopeid 0x20<link>
        ether ca:30:0c:da:97:62  txqueuelen 1000  (Ethernet)
        RX packets 5  bytes 434 (434.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 3  bytes 266 (266.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

dmesg showing the conflict with the stack running on dpdk:
IPv6: dpdk0: IPv6 duplicate address fe80::c830:cff:feda:9762 used by
ca:30:0c:da:97:62 detected!

> I can see 'macpair' is coming from "veth pair" above, but I don't think
> it is very explanatory in the context of tap. Do you have any more
> suggestion?
>
> Another concern is how to test this, tap PMD got multiple arguments now,
> and as the pmd keeps getting more updates and features, how can we sure
> this devarg usecase is not broken?

I'll take a look at the test-suite and try to come up with something better.

Thanks!