Re: Qemu monitor info tlb gives unable to encode message payload

On 12/8/21 12:09, Peter Krempa wrote: > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe. > > > On Wed, Dec 08, 2021 at 10:30:27 +0000, Philipp Klocke wrote: > > Hi, > > > > the command > > virsh qemu-monitor-command ubuntu_vm --hmp --cmd "info tlb" > > fails with "error: Unable to encode message payload". > > > > I found a bugtracker entry for a similiar error [1], but I don't if this is the same error (message too large). I also don't know how large an info tlb message is. > > Preferably I would not have to recompile libvirt just to issue this monitor command.. > Libvirt unfortunately limits strings to 4MiB: > > const REMOTE_STRING_MAX = 4194304; > > And the reply from qemu-monitor-command is a single string. Now > internally we process JSON messages up to 10 MiB so one could argue that > we should increase the size for the 'qemu-monitor-command' reply up to > 10MiB. This could be straightforward but it's questionable whether it's > worth it. Thanks for the clarification! I will try to go for the 2nd monitor then. > > Then I thought about circumventing the error by connecting directly to the qemu monitor via netcat, but I found a thread [2] that says I cannot add my own "-monitor tcp:..." to the Qemu commandline arguments. > IIRC at that point qemu wasn't able to handle two monitor connections. > At this point it is possible to have two concurrent connections to the > montitor. Obviously things may break and you get to keep the pieces if > it breaks. > > By adding: > > <qemu:commandline> > <qemu:arg value='-qmp'/> > <qemu:arg value='tcp:127.0.0.1:1235'/> > </qemu:commandline> When I add this to the config via virsh edit and then do a shutdown + reboot, I get a kernel panic. I put the corresponding dmesg log on gist: https://gist.github.com/klockeph/323f3e0d23a3254ef98a65fd7c8f5a1c