Re: [Qemu-devel] RFC: Proposal to add QEMU "Guest Environment Variables"

[Gabriel L. Somlo]

Hi Denis,

On Tue, Feb 03, 2015 at 10:14:03PM +0300, Denis V. Lunev wrote:
> On 03/02/15 22:09, Gabriel L. Somlo wrote:
>>
>>I'm interested in adding a way for a host to pass environment variables
>>into a qemu guest VM -- analogous to setting environment variables for
>>a process to access via getenv() and friends.
>>
>>The QEMU Guest Agent (QGA) does not appear to quite fit the bill, at
>>least not in its current form: The agent must have been successfully
>>started on the guest before the host would have to connect to it (in
>>a separate act from just starting the guest in the first place), and
>>get it to execute any hypothetical commands to configure or otherwise
>>influence the guest.
>>
>>For this functionality to really resemble the way environment variables
>>are used, environment information should be provided as part of the QEMU
>>command line, without the requirement to make a separate/subsequent
>>connection to the guest agent. For example:
>>
>>     qemu-system-x86_64 -guest-env="VAR1=value1;VAR2=value 2" -hda image.qcow2
>>
>>Once the guest is started, it should be possible to query the guest
>>environment with something like:
>>
>>     $ qemu-guest-env get VAR1
>>     value1
>>
>>     $ qemu-guest-env get VAR2
>>     value 2
>> [...]
> 
> I think that you can do this through guest write/guest exec commands.
> You can configure service start to perform it is a proper way through
> guest read/guest write and after that restart the agent.

Are these supposed to be commands issued from the qemu monitor prompt
(or qmp) ? My Google-fu didn't help too much either :)

The main idea is to be able to provide environment data to a guest
at start time (on the qemu command line), and not have to worry about
connecting back to it (via monitor prompt, qmp, if/when it starts the
guest agent, etc) to pass more information to it later on.

I'm probably misunderstanding what you said, though, so please
clarify...

Thanks much,
--Gabriel