Re: [Qemu-devel] [RFC][PATCH v6 00/23] virtagent: host/guest RPC communication agent

[Jes Sorensen]

On 01/17/11 14:14, Michael Roth wrote:
> These patches apply to master (1-14-2011), and can also be obtained from:
> git://repo.or.cz/qemu/mdroth.git virtagent_v6
> 
> CHANGES IN V6:
> 
>  - Added a sentinel value to reliably detect the start of an "http" hdr. Used 
> to skip past partially sent http content from previous "sessions"
>  - Added http hdr tag (currently hardcoded for testing, will switch to uuid) 
> to filter out valid-but-unexpected content in channel from previous "sessions"
>  - Added timeout mechanism to avoid hanging monitor when agent isn't running
>  - Added timed back-off on read's from a virtio-serial that result in ret=0 
> to avoid spinning if host isn't connected. 
>  - Added daemonize flags to qemu-va
>  - Added sane defaults for channel type and virtio-serial port path
>  - Various bug fixes for state machine/job handling logic
> 

Hi Michael,

I was running some testing here of virtagent and demoing it to some of
my colleagues and ran into a problem that raised an interesting question.

My test system was an older Fedora 11 system, which meant I had to
rebuild qemu, while I kept my test image and the qemu-va binary that I
had built on a Fedora 14 system.

What happened was that either due to the differences in platform, or
maybe due to lag in updating the windows over vnc, agent commands would
end up crashing qemu on the host. I am not sure whether this was due to
timeouts or incompatibility of the libraries, however the question
raised is whether it is good security wise to pull XMLRPC processing
into QEMU this way? Instead maybe it would be better to move it out into
it's own process that uses virtio-serial through QEMU for it's
communication?

In addition I think we need to consider a mechanism to make sure that
the host and guest side are really compatible.

Just a few things to consider.

Cheers,
Jes