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Re: [Libvir] [PATCH] add bootloader_args to libvirt xml to support bootloaders (like pypxeboot for example) that require arguments



On Tue, Jun 05, 2007 at 08:55:34AM -0400, Daniel Veillard wrote:
> On Tue, Jun 05, 2007 at 08:35:21AM -0400, Hugh Brock wrote:
> > Daniel Veillard wrote:
> > >  This all looks simple and clear except one point. 
> > >We used to process pygrub differently than other bootloaders, basically 
> > >testing
> > >for that value and making it a special case, ending up with 3 different 
> > >case:
> > >   - no bootloader (bootloader == 0)
> > >   - bootloader is not pygrub (bootloader == 1)
> > >   - bootloader is pygrub (bootloader == 2)
> > >I'm pretty sure we made that on purpose to avoid some problem, but I can't 
> > >remember why :-(. Your patch changes that and gets back to only 2 case, and
> > >I don't see an explanation of what changed to drop the special case. Can
> > >you explain why this was changed ? I also wonder what would happen if we 
> > >drop
> > >the new libvirt resulting from this say on a Fedora Core 6, would that 
> > >break
> > >pygrub in that environment due to the change ?
> > 
> > 
> > So this is an interesting question, and you may well be right that I 
> > have removed some special case that was at some point (or is still) 
> > important. Here is the full story as I understand it. In the old code, 
> > both the no-bootloader case (bootloader=0) and the non-pygrub case 
> > (bootloader=1) allow <kernel> and <initrd> in the xml along with the 
> > <bootloader> element. pygrub takes no such arguments, so if that was the 
> > bootloader being used (bootloader=2) the <kernel> and <initrd> were 
> > omitted.
> > 
> > As you can imagine when I saw this code my first thought was "what the 
> > hell is this" <g>, so I checked with Dan. We were both unable to imagine 
> > a scenario in which having <kernel> and <initrd> in the xml along with 
> > <bootloader> was useful, since if you know what kernel and initrd you 
> > want to boot (for the paravirt case, of course), you don't need a 
> > bootloader. We also didn't much like having a check for "pygrub" 
> > hardcoded in libvirt, especially since I would have had to extend it to 
> > be "pygrub" || "pypxeboot" (yuck).
> > 
> > If we really do need this special case then I'm more than happy to put 
> > it (or some less nasty version of it) back. I agree that it does have 
> > the look of something that was added for a specific edge case.
> 
>   I remember the 'yuck but I don't see any other way' feeling when we
> added this. But since 1/ I can't remember precisely 2/ you and Dan looked
> at it and couldn't find either, I'm fine taking the very small risk of breaking
> something in an older release. Libvirt is by essence a place where nasty
> tricks like this will pile over time, and while we really try to keep
> compatibility, if really we can find/remember why one could be needed
> cleanup makes sense.
>   Let's apply the patch then ! Will do shortly unless you disagree,

  okay, commited,

   thanks !

Daniel

-- 
Red Hat Virtualization group http://redhat.com/virtualization/
Daniel Veillard      | virtualization library  http://libvirt.org/
veillard redhat com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine  http://rpmfind.net/


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