On Thu, 2014-02-06 at 17:30 +0400, Michael Tokarev wrote: > 06.02.2014 17:15, Ian Campbell wrote: > > On Thu, 2014-02-06 at 17:08 +0400, Michael Tokarev wrote: > >> 06.02.2014 12:50, Gerd Hoffmann wrote: > [] > >>> As far I know xen has its own seabios builds anyway as they > >>> have to add hvmloader to the mix. Thats why it has been > >>> turned off in the upstream blob builds, nobody will use these > >>> with xen anyway. > >> > >> Thank you Gerd for the answer. Ian, can you give some light > >> here, what is still missing in seabios for xen? Because, > >> well, .. > > > > Nothing is missing in seabios. > > > > The above patch is a fix to Xen not SeaBIOS, which lets it work > > correctly regardless of the size of the seabios binary. > > > > There is no need to do anything other than apply that fix to the Xen > > packages (perhaps by upgrading to 4.3.1) AFAIK. > > Okay. That is good to know, because it started to become > quite confusing :) > > Yes I understand the xen hvmloader change is necessary for > xen to support larger bios sizes, and new full-blown bios > is larger than 128Kb. > > [] > >> (And yes I know about > >> > >> http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=5f2875739beef3a75c7a7e8579b6cbcb464e61b3 > >> which talks about >128kb bios size. This is actually exactly > >> the same issue which I'm trying to address now, from a few PoVs: > >> qemu now builds/uses stripped-down bios for older (pre-2.0) machine > >> types, and that stripped-down version does not include Xen bits > >> in order to fit in 128Kb, because with xen it doesn't fit anymore. > >> Maybe we should start building special xen variant of seabios -- > >> stripped down but WITH xen. Oh well.) > > > > Why is this stripped down SeaBIOS needed? > > Because it fits into 128Kb, while complete build doesn't. > And when the bios size grows (provided that software - > xen and qemu - actually support this), it breaks guest > migration between old and new systems. > > > Is there some reason the Xen build can't pickup the non-stripped down > > (post-2.0) SeaBIOS? > > The question is exactly about old systems. Qemu has an option, > -M foo. Right now, if foo is less than 2.0 (the upcoming release), > it picks up the old small and now stripped-down verion of seabios. > For new versions - like -M pc-2.0, or by default - it uses the > new larger bios with all features. > > But I've no idea if xen actually uses or cares about -M to start > with. Qemu supports it for 2 things: migration, and keeping, say, > windows guests activated across version changes (with variable > success on both fronts :)
Xen only supports migration from version N to N+1, and since this issue is fixed it should be fine. I'm not sure why the BIOS size is relevant to migration anyway, Xen doesn't load a new BIOS on the target host, the BIOS image is part of the migrated RAM. Ian.
