Re: [libvirt PATCH 4/9] conf: add passt XML additions to schema

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 12 Jan 2023 09:45:39 -0500
Laine Stump <laine@redhat.com> wrote:

> On 1/11/23 1:33 PM, Daniel P. Berrangé wrote:
> > On Sun, Jan 08, 2023 at 11:11:07PM -0500, Laine Stump wrote:  
> >> Initial support for network devices using passt (https://passt.top)
> >> for the backend connection will require:
> >>
> >> * new attributes of the <backend> subelement:
> >>    * "type" that can have the value "passt" (to differentiate from
> >>      slirp, because both slirp and passt will use <interface  
> >>      type='user'>)  
> >>    * "logFile" (a path to a file that passt should use for its logging)
> >>    * "upstream" (a netdev name, e.g. "eth0").  
> > 
> > IMHO this attribute is inappropriate for <backend>....
> >   
> [...]
> >> +    <interface type='user'>
> >> +      <mac address='00:11:22:33:44:55'/>
> >> +      <ip address='172.17.2.0' family='ipv4' prefix='24'/>
> >> +      <ip address='2001:db8:ac10:fd01::feed' family='ipv6'/>
> >> +      <portForward proto='tcp' address='2001:db8:ac10:fd01::1:10'>
> >> +        <range start='22' to='2022'/>
> >> +        <range start='1000' end='1050'/>
> >> +        <range start='1020' exclude='yes'/>
> >> +        <range start='1030' end='1040' exclude='yes'/>
> >> +      </portForward>
> >> +      <portForward proto='udp' address='1.2.3.4' dev='eth0'>
> >> +        <range start='5000' end='5020' to='6000'/>
> >> +        <range start='5010' end='5015' exclude='yes'/>
> >> +      </portForward>
> >> +      <portForward proto='tcp'>
> >> +        <range start='80'/>
> >> +      </portForward>
> >> +      <portForward proto='tcp'>
> >> +        <range start='443' to='344'/>
> >> +      </portForward>
> >> +      <model type='rtl8139'/>
> >> +      <backend type='passt' logFile='/var/log/loglaw.blog' upstream='eth42'/>  
> > 
> > I don't think that 'upstream' is really describing a property of the
> > backend.
> > 
> > This is expressing a traffic routing restriction for the 'user'
> > networking type. IMHO it should probably be using the existing
> > <source dev="xxxx"/> element, that is currently used by the
> > 'direct' networking type.  
> 
> I'm still not sure *exactly* what it does; it apparently grabs the 
> routes that are fed to the guest from the given host interface; I should 
> probably ask Stefano to explain it to me again (he described it once, 
> but that was along with explanations of several other things).

Yes, it's pretty much that... recycling from the man page:

       -i, --interface name
              Use host interface name to derive addresses and routes.  Default
              is  to use the interfaces with the first default routes for each
              IP version.

It's not actually a routing restriction -- passt can't do that. The
only interface binding that passt implements (with Linux kernel
versions >= 5.7) is an optional bound interface specification for port
forwarding.

> So it's not *exactly* the same as <source dev='xxx'/> for type='direct' 
> (which determines the link-level connection rather than IP routing), but 
> definitely very similar.

Right, I think so too, and "source" is probably a good name for that in
any case.

-- 
Stefano