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Re: [libvirt-users] virsh edit problems



On 09/26/2011 02:30 PM, Robin Lee Powell wrote:
What I have now:

     <serial type='pty'>
       <target port='0'/>
     </serial>
     <console type='pty'>
       <target type='serial' port='0'/>
     </console>

That's correct for the persistent config.


No matter what I change, whether I use "virsh edit"

Good.

or edit the
files directly,

Don't do that. It won't work, and you risk corrupting things by going behind libvirt's back.

> even with libvirt off, as soon as libvirt notices
(i.e. when I turn it back on) my changes get blown away and it ends
up looking just like the above.  Even as simple a thing as changing
the port number, or removing the console, or adding a second
serial... all gone.

That's an indication that the things you are adding are not essential to the persistent config. 'virsh edit' prunes your input back into the xml essential to what libvirt needed, so if your edits didn't stick, then they weren't making a difference.


Oh, wait, that's not quite true; adding a second serial *does* work.
But nothing else I've tried does.

What I'm actually trying to do is copy the docs
http://libvirt.org/formatdomain.html#elementsConsole more closely
and specify my own source paths; I'm worried that the serial and the
console are somehow ending up in the same place and maybe that's
causing my problem?

What I've been trying to do is something like:

     <serial type='pty'>
       <source path='/dev/pts/3'/>
       <target port='0'/>
     </serial>

Ah - maybe I can explain that issue. For pty devices, <source path=.../> is computed at runtime, once libvirt has actually allocated a pty from the host (which pty gets allocated depends on what else has been going on in your host prior to starting your guest). Since the pty allocated is dependent on various runtime factors, there is no way to pre-allocate a fixed pty value - so this <source> element is something that 'virsh dumpxml' outputs to show you which pty libvirt allocated, but where you have no control (and no need to control) which pty to attempt to allocate. And libvirt is merely stripping the unused <source> from your persistent config because it doesn't make sense in a persistent context.

     <console type='pty'>
       <source path='/dev/pts/4'/>
       <target port='0'/>
     </console>

And it just won't stick.  Maybe that's not even my problem, but it's
not showing any errors, and it's annoying me and I'd like to
understand why.

Hopefully my explanation helps, but feel free to ask more questions as needed. Perhaps this is a case of me answering your stated question rather than your implied question (that is, I answered why <source> is disappearing, but not how to get a console to your guest working in the first place).

--
Eric Blake   eblake redhat com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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