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 08:35:21AM -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,