Re: Support for equivalent to slirp guestfwd

On Thu, 26 Feb 2026 11:31:15 -0500 Peter Foley wrote:

On Thu, Feb 26, 2026 at 7:47 AM Stefano Brivio wrote:

...

...there's ongoing effort to make this more flexible, by adding support for generic NAT rules (https://bugs.passt.top/show_bug.cgi?id=140) so that you can specifically map different ports and addresses to specific ports and addresses. And do so dynamically, at runtime, too.

We now have a rather generic "forwarding rules" table implementation, even if not entirely complete:

https://archives.passt.top/passt-dev/20260116005926.616085-1-david@gibson.dr...

and a very rudimentary draft of pesto(1), the client that would enable configuring all that at runtime (I'm working on it these days):

https://archives.passt.top/passt-dev/20260204234209.455262-1-sbrivio@redhat....

...there's quite a bit left to do, and patches are warmly welcome.

Alright, that's about what I expected.

We currently heavily rely on stuff like guestfwd=udp:[::]:1000-udp:[::1]:14418, where we want to redirect all outbound traffic from the guest to port 1000 to a different dynamically allocated port where a server binary is listening on the host.

Hah, I see. Somewhat curiously, that's the first time I see this kind of usage being reported. I knew libslirp could do it but I wasn't aware of any concrete usage.

We don't need runtime configuration, just the ability to specify everything statically when starting qemu.

That will come pretty much for free once we have generic code for the runtime updates, I think.

I can't promise anything, but I'll see if this is something other people on my team would have cycles to help out with.

Thanks! -- Stefano