[ovirt-devel] execCmd() and storing stdout and stderr in log file

[Francesco Romani]

----- Original Message -----
> From: "Yaniv Bronheim" <ybronhei at redhat.com>
> To: "Tomáš Golembiovský" <tgolembi at redhat.com>
> Cc: "devel" <devel at ovirt.org>
> Sent: Monday, July 11, 2016 6:28:10 PM
> Subject: Re: [ovirt-devel] execCmd() and storing stdout and stderr in log	file
> 
> 
> 
> On Mon, Jul 11, 2016 at 12:53 PM, Tomáš Golembiovský < tgolembi at redhat.com >
> wrote:
> 
> 
> On Wed, 6 Jul 2016 18:37:54 +0300
> Yaniv Bronheim < ybronhei at redhat.com > wrote:
> 
> > On Wed, Jul 6, 2016 at 5:07 PM, Tomáš Golembiovský < tgolembi at redhat.com >
> > wrote:
> > 
> > > 
> > > Merging stdout and stderr to one can POpen do for us, I belive. Any
> > > logging can indeed be done as a wrapper around execCmd.
> > 
> > saving stdout and err to log while the process is running is useful only
> > for your purpose currently. using asyncproc as you do now in v2v allows you
> > to to run a process and monitor it.. can you use overriding of aysncProc
> > wrapper for your needs instead of changing cpopen or execcmd code?
> 
> I am not talking about CPOpen. I meant that when calling
> `subprocess.Popen`, you can pass it `stderr=subprocess.STDOUT` argument
> and it will handle the FD redirection (stream merging). To me it seems
> like a proper way of doing this.
> 
> 
> In vdsm we currently use cpopen to start external process - as
> multiprocess.popen in py2 is buggy. using execCmd doesn't provide stderr and
> stdout parameters to modify. but you can use CPopen directly and override
> stderr.
> Over py3 we import the standard multiprocess.Popen. basically if its actually
> useful you can add those parameters to execCmd

Good news about cpopen!

Is it a good idea to add even more parameters to execCmd? Let's discuss this.

another approach I could think of is https://gerrit.ovirt.org/#/c/60660/
I'm not that proud of 60660 either, this is why it is a draft :\

So I've been in touch with Tomas, and he kindly tried to rebase his code
on top of my 60660, but looks like  he was biten by issues fixed in
https://gerrit.ovirt.org/#/c/59181/
https://gerrit.ovirt.org/#/c/59095/

I think leveraging cpopen is a good way, it is simple enough and it doesn't
hurt our plans to eventually move to subprocess.

Thoughts welcome

Thanks and bests,

-- 
Francesco Romani
RedHat Engineering Virtualization R & D
Phone: 8261328
IRC: fromani