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From Michael Ryan <mpr...@alumni.cmu.edu>
Subject Re: fork() exec() in qemu.py
Date Fri, 12 Nov 2010 03:22:15 GMT
If you want to replace fork() + exec() with subprocess, be my guest -- I 
was just saying that trying to use subprocess.Popen directly (which 
returns an object), doesn't buy you anything extra -- you still need to 
read the controlling pty from output and record the PID in case of NM 
failure or rolling restart.

- Michael

On 11/11/2010 7:26 PM, Michael Stroucken wrote:
> Michael Ryan wrote:
>> How do you create a subprocess object from a PID? If the NM gets
>> restarted, it needs to be able to manage the processes. It was mainly
>> for consistency -- so that some VMs weren't managed by Popen objects
>> and others by PIDs.
>
> So as I see it, the code uses fork and exec to start the qemu process in
> the background and record the pid. On initialization, the NM collects
> the information from storage into ControlledVMs to resume control. In
> all cases, ControlledVMs contains the information of running VMs.
>
> I don't think you'd need to create a subprocess object. You collect it
> when starting a VM, but save the data into ControlledVMs right
> afterwards (as is done now) and continue.
>
> Greetings,
> Michael.

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