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Re: [libvirt] [Qemu-devel] Re: Supporting hypervisor specific APIs in libvirt

On 03/22/10 22:53, Anthony Liguori wrote:
On 03/22/2010 04:33 PM, Gerd Hoffmann wrote:
libvirt is very unfriendly to qemu hackers. There is no easy way to
add command line switches. There is no easy way to get access to the
monitor. I can get it done by pointing <emulator> to a wrapper script
and mangle the qemu command line there. But this sucks big time. And
it doesn't integrate with libvirt at all.

It's not just developers. As we're doing deployments of qemu/kvm, we
keep running into the same problem. We realize that we need to use a
feature of qemu/kvm that isn't modelled by libvirt today. I've gone as
far as to temporarily pausing libvirtd, finding the pty fd from
/proc/<pid>, and hijacking the monitor session temporarily.

One problem I have found, and I am not sure how to fix this in this
context. Sometimes when hacking on qemu, I want to try out a new
qemu binary on an existing image, without replacing the system wide
one and may want to pass new command line flags for testing those, plus
have access to the monitor.

What I do now is to look at the command line arguments of a guest using
ps and try and mimic it, but due to the random magic ptys and other
stuff, it's practically impossible to replicate a libvirt spawned qemu
on the command line. I end up having a somewhat similar command line
with everything removed that I cannot replicate.

I find it a real problem that libvirt tries to wrap things to the point
that an ordinary human cannot read, modify it's configuration or do a
simple command line spawn to replicate it, but as I said, I am not sure
how to solve the problem.


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