On Thu, Mar 20, 2025 at 08:56:04AM +0100, Maximilian Immanuel Brandtner wrote:
> I've been working on an RFC patch-set to implement resizing for
> consoles in QEMU. Now that the patch-set is in review I've turned my
> attention to bringing this feature to libvirt.
Can you point to the QEMU patchset URL ?
> With the QEMU patch-set there are two ways to resize a pty chardev.
> 1. send a TIOCSWINSZ ioctl
> 2. send a QMP msg
>
> The first approach doesn't work under Libvirt. Pty chardevs are proxied
> over a FIFO meaning the ioctl wouldn't get to libvirt. Furthermore,
> this approach is incompatible with remote management which libvirt
> seems to go to great lengths to support.
So we have the flow
virsh console (or equiv mgmt equiv)
-> virStream
-> libvirtd/virtqemud
-> virStream
-> PTY
-> QEMU chardev
-> guest serial port / paravirt console
NB I've always wanted to extend our console stream handling to support
UNIX socket / TCP socket chardev instead of the PTY, as the connection
semantics are so much saner to deal with.
> Sending a QMP message is a QEMU specific feature. It seems to me that
> adding a new handle (something like domainResizeConsole) would have to
> be added to the virHypervisorDriver struct. It would be really nifty if
> the resize handle could be implemented in the virStream, however it
> seems that all the virStreamDriver handlers are common code (aka shared
> across all hypervisors). From what I've seen it seems that the only way
> to switch from common code to hypervisor specific code would be over
> the virHypervisorDriver. As it stands it seems to me that the best
> course of action would be adding a new handle to the
> virHypervisorDriver, but I'm unsure whether that's really the right
> call.
How is the window resize supposed to be passed to the QEMU chardev
backend for the different chardev backend types ?
> TLDR I have the following 2 questions:
> - Should the resize handle be implemented in the virHypervisorDriver
> directly or in the virStreamDriver?
Unclear currently. I did think about this a long while back and tried
to hack something into virStream, but never completed it and it was
not as simple as it first seemed
> - Is there a way to get the QMP alias of a chardev from a virStream?
No, currently the stream only knows about the underlying host OS channel,
nothing about the hypervisor
With regards,
Daniel
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