Re: [libvirt] Serial connection between guests

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..

Maybe it could be handled like Ethernet network is. You add a cable, and on cable specs you define which dom/port is connected to that end. I tried to think on an UI that would allow this but all my ideas are confusing. > For more details on how this works and what you can use, see the > documentation [1]. Beware that if it's the only serial port n the > guest, it will become a console, so you might want to add it instead > of modifying an existing one. That's probably what kept it from working here for a long time hehe took me a while to notice that. > Also, the examples are done without any security labels in mind. If > you use SELinux, for example, you'll probably need to adjust the > <seclabel/> for the sockets, see the docs [2] for details. Thanks, Marcelo > > Martin > > [1] https://libvirt.org/formatdomain.html#elementCharChannel > [2] https://libvirt.org/formatdomain.html#seclabel > > >What do you think? My usage is for virtualizing TAHI: > >http://networktest.sourceforge.net/usage.html > >I need 2 ethernet links plus a serial one, which TAHI can't break while > >running the tests. > > > >I didn't think this regarding multi-platform & all.. just sharing the > >idea/need. > > > >Thanks, > >Marcelo > > > >-- > >libvir-list mailing list > &gt;libvir-list(a)redhat.com > >https://www.redhat.com/mailman/listinfo/libvir-list