Re: [Qemu-discuss] How can we install RPMs in guest VM from host machine using QEMU guest agents

[Mike Lovell]

On 06/12/2014 04:32 AM, Puneet wrote:
> Hi,
>
> I want to be able to install RPM packages (available in host system at some
> path) to the guest VM and want this facility to be available as a tool.
>
> I am thinking of having a gemu guest agent (qemu-ga) running inside guest
> VM. I did not find any available command ("virsh qemu-agent-command
> <guest_vm> ...") which can do the same.
>
> I am planning to write a command in qemu guest agent, which I can invoke
> from virsh like below.
>
>      "virsh qemu-agent-command vm_01          \
>          '{"execute":"guest-rpm-install",     \
>            "arguments":{"path":"/usr/local/bin/ABC.rpm"}}
>        
> I am able to pass arguments from host to guest VM but how am I supposed to
> pass the whole RPM image from host to guest (which the guest agent can
> receive and install)?

according to the schema for the guest agent commands [1], there are 
several commands for opening and writing a file in the guest. you could 
use those to transfer a file to the guest. it would be something like 
guest-file-open, one or more guest-file-write commands to transfer bits 
of data read from a file on the host, and then a guest-file-close. i 
don't know if libvirt would support this so you would probably have to 
implement a program to run on the host that communicates with the guest 
agent to transfer the file. there is a script in the qemu source tree 
that has the same basic idea for reading a file from the guest in 
python. [2] look at the QemuGuestAgentClient.read function. it could 
probably be easily modified to transfer a file to the guest.

the harder part is going to be executing rpm, yum, or any other command 
in the guest. the command schema doesn't currently list a command to 
execute an arbitrary executable in the guest so you would either need to 
implement a command to execute an arbitrary executable or specifically 
execute the rpm or yum commands you need. the later would be a little 
better from a security perspective. and of course rpm wont work on your 
windows vms though the same basic idea might apply.

mike

[1] http://git.qemu-project.org/?p=qemu.git;a=blob;f=qga/qapi-schema.json
[2] 
http://git.qemu-project.org/?p=qemu.git;a=blob;f=scripts/qmp/qemu-ga-client