Re: [libvirt] Serial connection between guests

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