From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47906) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WBP26-0001Gv-Em for qemu-devel@nongnu.org; Thu, 06 Feb 2014 08:30:27 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WBP20-0001FL-Fj for qemu-devel@nongnu.org; Thu, 06 Feb 2014 08:30:22 -0500 Received: from isrv.corpit.ru ([86.62.121.231]:40488) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WBP20-0001FD-8o for qemu-devel@nongnu.org; Thu, 06 Feb 2014 08:30:16 -0500 Message-ID: <52F38E65.4010003@msgid.tls.msk.ru> Date: Thu, 06 Feb 2014 17:30:13 +0400 From: Michael Tokarev MIME-Version: 1.0 References: <52F347C3.9030600@msgid.tls.msk.ru> <1391676619.17309.39.camel@nilsson.home.kraxel.org> <52F38939.8010704@msgid.tls.msk.ru> <1391692554.25128.7.camel@kazak.uk.xensource.com> In-Reply-To: <1391692554.25128.7.camel@kazak.uk.xensource.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] 128Kb bios size and older machines? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Ian Campbell Cc: Gerd Hoffmann , qemu-devel 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 :) Thanks, /mjt