Re: Serial connection between guests

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On Tue, Jul 14, 2015 at 05:58:05PM +0200, Martin Kletzander wrote:
> On Tue, Jul 14, 2015 at 08:25:27AM -0300, Marcelo Ricardo Leitner wrote:
> >Hi,
> >
> >On Tue, Jul 14, 2015 at 09:52:12AM +0200, Martin Kletzander wrote:
> >>On Fri, Jul 10, 2015 at 04:28:46PM -0300, Marcelo Ricardo Leitner wrote:
> >>>Hi,
> >>>
> >>>(I'm not subscribed to the list, please keep me on Cc)
> >>>
> >>>I'm attempting to get a serial link between two guests, same hypervisor.
> >>>The only practical way I could find is to add a serial port using a pty
> >>>to a guest and then manually connecting to the serial (console in my
> >>>case) of the other guest using socat in the hypervisor.
> >>>
> >>>Then it made me think.. we could have this implemented at libvirt level.
> >>>We could have a serial port on which we choose pty, udp, tcp, etc, and
> >>>also a serial port from another guest, so that libvirt would handle
> >>>socat start/stop automatically as both guests come up/down. Maybe
> >>>libvirt could even do something smarter than that, maybe it can avoid
> >>>socat somehow.
> >>>
> >>
> >>You can have one domain with serial port that will listen on some
> >>interface (unix socket, ip and port, whatever) and then have the
> >>second one connect to it.  That could be done for example like this:
> >>
> >>XML snippet of device for domain A:
> >> <serial type='file'>
> >>   <source mode='bind' path='/tmp/tahi.sock'/>
> >>   <target port='1'/>
> >> </serial>
> >>
> >>XML snippet of device for domain B:
> >> <serial type='file'>
> >>   <source mode='connect' path='/tmp/tahi.sock'/>
> >>   <target port='1'/>
> >> </serial>
> >>
> >>This way you need to make sure domain A is started when you are
> >>starting domain B, so it can connect to the socket that was created by
> >>domain A.  If you don't want to depend on the order of domains being
> >
> >I'd like to avoid that as much as possible. (though I failed to connect
> >the serial interfaces through libvirt with any of the configs, tcp,
> >unix, etc..) perhaps due to the console thing you mentioned below.
> >
> >>started, you can use for example socat for that:
> >>
> >>XML snippet of device for domain A:
> >> <serial type='file'>
> >>   <source mode='bind' path='/tmp/tahi-domA.sock'/>
> >>   <target port='1'/>
> >> </serial>
> >>
> >>XML snippet of device for domain B:
> >> <serial type='file'>
> >>   <source mode='bind' path='/tmp/tahi-domB.sock'/>
> >>   <target port='1'/>
> >> </serial>
> >>
> >>And then run socat as:
> >> socat unix:/tmp/tahi-domA.sock unix:/tmp/tahi-domB.sock
> >
> >That's what I was doing in the end. It also allows me to change the
> >connection on the fly if needed, but I have to keep an eye on socat. I
> >was thinking if we could have something more automatic for it.
> >
> >Like, if I have domA and domB connected through a serial link using
> >socat, and I reboot the hypervisor, I wanted the socat to come back
> >automatically. Same if it dies..
> >
> 
> You can use hook for that, probably
> 
> https://libvirt.org/hooks.html

Looks very interesting, thanks!

  Marcelo

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