Re: [Qemu-devel] QEMU patch to allow VM introspection via libvmi

[Eric Blake]

On 10/23/2015 08:44 AM, Valerio Aimale wrote:

> 
> Libvmi dependence on virsh is so strict, that libvmi does not even know
> if the QEMU VM has an open qmp unix socket or inet socket, to send
> commands through. Thus, libvmi sends qmp commands (to query registers,
> as an example) via
> 
> virsh qemu-monitor-command Windows10B '{"execute":
> "human-monitor-command", "arguments": {"command-line": "info registers"}}'

This is an unsupported back door of libvirt; you should really also
consider enhancing libvirt to add a formal API to expose this
information so that you don't have to resort to the monitor back door.
But that's a topic for the libvirt list.


> 
> so that libvmi can find the rendezvous unix/inet address and sends
> commands through that. As of now, each qmp commands requires a popen()
> that forks virsh, which compounds to the slowness.

No, don't blame virsh for your slowness.  Write your own C program that
links against libvirt.so, and which holds and reuses a persistent
connection, using the same libvirt APIs as would be used by virsh.  All
the overhead of spawning a shell to spawn virsh to open a fresh
connection for each command will go away.  Any solution that uses
popen() to virsh is _screaming_ to be rewritten to use libvirt.so natively.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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