[libvirt-users] redirecting guest stdio to the host

[Eric Blake]

On 05/28/2014 09:14 AM, Alexander Binun wrote:

[can you convince your mailer to wrap long lines?]

> 
> I have a program running on a VM guest. Its output is valuable (for VM introspection) so I want to let the host module know about it. I prefer to redirect  ' stdio" of a guest into a device at the host (a text file or my device that has the name "mydev" 
> and the driver is written for it). 
> 
> I have the XML definition file for my VM in /etc/libvirt/qemu. I have added the section:
> 
>     <serial type="file">
>       <source path="/var/log/vm/vml.log"/>
>       <target port="0"/>
>     </serial>
>   
> into the /devices section.
> 
> That is I want the stdio to be streamed into the file /var/log/vm/vml.log at the host.
> 
> Then I run simple textual commands at the guest (ls, pwd and so on).

How are you getting into your guest to run those commands?  Did you
connect to your guest's serial console, or is it in a gui window, or via
an ssh session, or...?  Are you sure the commands you are executing have
the guest's /dev/ttyS0 as their stdout?

> But I do not see /var/log/vm/vml.log created at the host.

I'm not sure whether libvirt will pre-create the file, or whether it
insists that the file already exists. Maybe others can chime in.  I know
Dave Allan has done some work with python scripts that faithfully
capture all text output to the guest's serial console, although I don't
have a handy link to that sample script.

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

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