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

On Thu, 12 Jan 2023 09:45:39 -0500
Laine Stump <laine(a)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