Re: [cobbler-devel] [PATCH 0/5] Port koan from virtinst to virt-install command

[Michael DeHaan]

On Monday, February 6, 2012 at 2:55 PM, Cole Robinson wrote:
> On 02/06/2012 12:34 PM, Michael DeHaan wrote:
> > On Monday, February 6, 2012 at 11:37 AM, Cole Robinson wrote:
> > > On 02/06/2012 10:58 AM, Michael DeHaan wrote:
> > > > Cole --
> > > >
> > > > What's the workaround to auto-start Xen PV's? (or is there not a way?)
> > > >
> > > > Seems like we could just implement this however needed (if xenpv… do this
> > > > instead…), if virtinstall won't do it for us.
> > >
> > > The autostarting code could just be conditionally enabled if virt-install is
> > > new enough (just a grep of the help output) so that's not the issue.
> > >
> > > The issue is that current koan code manually passed a kernel + initrd for the
> > > PV guest to boot. That's the only install scenario for PV guests AFAICT. And
> > > this is only available via the virt-install in a version newer than what's in
> > > RHEL5.
> >
> > That's also how the virt installs work for everything else in koan, including
> > qemu/KVM.
> >
> > (Maybe I'm misunderstanding something?)
>
> This is my understanding of the current code.
>
> Xen FV: always does a PXE boot (so guest is actually talking to PXE server):
> https://github.com/cobbler/cobbler/blob/master/koan/xencreate.py#L80
>
> Xen PV: Libvirt tells the guest to boot directly off the kernel/initrd pair
> specified in profile_data["kernel_local"] and profile_data["initrd_local"]:
> https://github.com/cobbler/cobbler/blob/master/koan/xencreate.py#L88
>
> (are those kernel_local + initrd_local values filled in by cobbler or does the
> user need to manually specify them?)
>
> QEMU/KVM has two install options:
>
> if profile_data["file"] is present, boot off it like a cdrom:
> https://github.com/cobbler/cobbler/blob/master/koan/qcreate.py#L101

Don't think I care about this one, meaning I think we could get rid of it.
> if profile_data["install_tree"] is present, pass the URL off to virtinst and
> have it use it's tree probing to fetch kernel + initrd:
> https://github.com/cobbler/cobbler/blob/master/koan/qcreate.py#L121

Ugh yes, I believe that was required as it didn't support the other at the time or something.
It has been a while.   I had to work around a lot of inconsistencies and seem to recall thinking
it was easier than it was :)
> My implementation preserves this behavior, but in reality Xen FV and Qemu can
> all boot from tree/kernel, cdrom, and pxe. Xen pv can only boot from
> tree/kernel (which is the same thing basically).

Requiring PXE is disadvantageous to those that don't have DHCP, so yeah, I don't think that should
be the default way.
> My suggestion was to adapt xen pv to behave as qemu does with "install_tree".

Sounds reasonable.
> > > The workaround could be to make PV installs work like qcreate install_location
> > > installs, which is basically the same as direct kernel/initrd boot but you
> > > rely on virt-install to pull the kernel/initrd from the install tree.
> >
> > Just trying to make sure this wouldn't break anyone.
> >
> > The install tree location isn't actually required in Cobbler, it's only a
> > parameter to the kickstart … Are you saying we'd have to use the install
> > tree method *only* for Xen PV? If so, that might be an acceptable
> > limitation… if Xen FV or qemu/KVM requires the tree to find the
> > kernel/initrd that seems bad to me, because we deal with a lot of arbitrary
> > distros that express install tree locations in different ways.
> > ks_meta["tree"] gives you this if someone had ran "Cobbler import" previously.
> >
> > If we can avoid using that when we don't have to, that would be good…
> > > Since
> > > cobbler tracks this info it would probably 'just work' with a tiny patch but
> > > someone would need to test. And this has been supported on virt-install
> > > command line since probably rhel5.1
> >
> > "it" == making autostart work for Xen PV, right?
>
> No, autostart is not the issue here. The issue is getting guests to actually
> install. The autostart piece is just recent functionality to cobbler that
> currently brok all installs on RHEL5 host. Fixing this would be a fairly
> trivial patch on top of current koan or my code.
>
> The more interesting piece is making xen PV installs actually work on RHEL5
> where virt-install is not new enough to provide the cli option needed to have
> parity with current xen PV installation, which requires passing a local kernel
> initrd path to boot from.
>
> Sorry if that isn't clear.

nod, ok, all sounds reasonable -- send me a pull request or whatever with what you think sounds reasonable -- ideally after trying it out live, and we'll merge it in.

Thanks for the explanations.
> Thanks,
> Cole