On Tue, 2013-06-18 at 19:56 +0100, Stefano Stabellini wrote: > On Fri, 14 Jun 2013, Paul Durrant wrote: > > > -----Original Message----- > > > From: Paolo Bonzini [mailto:paolo.bonz...@gmail.com] On Behalf Of Paolo > > > Bonzini > > > Sent: 14 June 2013 15:58 > > > To: Paul Durrant > > > Cc: Ian Campbell; Stefano Stabellini; qemu-devel@nongnu.org; xen- > > > de...@lists.xen.org > > > Subject: Re: [Xen-devel] [PATCH] Remove hardcoded xen-platform device > > > initialization > > > > > > Il 14/06/2013 10:11, Paul Durrant ha scritto: > > > > I think we're still going to need -M xenpv, I think; it's quite > > > > distinct from pc. > > > > > > Of course! Even more: "-M xenpv" should be reused on ARM. > > > > > > > I guess we could use -M pc for HVM and gate the > > > > accel code as you suggest but, if that's the way we're going, it > > > > would seem more logical just to ditch the accel code for xenpv > > > > completely (assuming we can do all we need from the machine init) and > > > > then use -M pc -accel=xen for HVM guests going forward. > > > > > > There is common code between pv and fv, and that one definitely belongs > > > in xen_init. Most fv-only code probably should be in pc_init. The rest > > > should move to xen_init though, because it would apply just as well for > > > example to Q35. It's a bit ugly to have fv-only code there, but it's > > > better than having a Xen-specific machine type. Xen/KVM/TCG should be > > > as similar as possible at the QEMU level, any difference should be > > > handled in the toolstack. > > > > > > > But that does > > > > rather screw up my autodiscovery plans because I would not know, for > > > > a given qemu binary, which machine type to use. > > > > > > There's no need for that. 4.4 can just use "-M pc" unconditionally, > > > <=4.3 will just use "-M xenfv" unconditionally. > > > > > > > If I create a new > > > > xenfv-2.0 machine type though I *can* do auto discovery... in which > > > > case do we need the -accel=xen option at all? > > > > > > Yes. Please try not do things differently from other accelerators. > > > > > > > Ok. I guess we can have the ability to override the machine type in the VM > > config, so you could still kick off an older qemu with a newer libxl - but > > it sounds like the auto-discovery idea is a no-go then. > > xenfv-2.0 is a bad idea, like Paolo wrote, it should be possible to just > use -M pc for HVM guests and retain -M xenpv for pv guests. > > However it seems to me that we also need a way in libxl to find out > whether QEMU is new enough for us to be able to use -M pc. > We can't just assume that users will be able to figure out the magic > rune they need to write in the VM config file to solve their VM crash at > boot problem.
What crash at boot problem? > We could spawn an instance of QEMU just to figure out the QEMU version > but we certainly cannot do that every time we start a new VM. > Once we figure out the QEMU version the first time we could write it to > xenstore so that the next time we don't have to go through the same > process again. Due to the device_model_override we might need to make this per-path. You'd also likely need to store mtime or something in case qemu gets upgraded, although perhaps that is getting unnecessarily picky... Ian.
