> -----Original Message----- > From: Stefano Stabellini [mailto:stefano.stabell...@eu.citrix.com] > Sent: 23 May 2014 12:37 > To: Paul Durrant > Cc: Stefano Stabellini; Gerd Hoffmann; Paolo Bonzini; qemu- > de...@nongnu.org; Anthony Liguori; m...@redhat.com; Anthony Perard > Subject: RE: [PATCH] xen: make xen-platform a default device > > On Fri, 23 May 2014, Paul Durrant wrote: > > > -----Original Message----- > > > From: Stefano Stabellini [mailto:stefano.stabell...@eu.citrix.com] > > > Sent: 23 May 2014 11:11 > > > To: Paul Durrant > > > Cc: Stefano Stabellini; Gerd Hoffmann; Paolo Bonzini; qemu- > > > de...@nongnu.org; Anthony Liguori; m...@redhat.com > > > Subject: RE: [PATCH] xen: make xen-platform a default device > > > > > > On Fri, 23 May 2014, Paul Durrant wrote: > > > > > -----Original Message----- > > > > > From: Stefano Stabellini [mailto:stefano.stabell...@eu.citrix.com] > > > > > Sent: 22 May 2014 14:57 > > > > > To: Gerd Hoffmann > > > > > Cc: Paolo Bonzini; Stefano Stabellini; Paul Durrant; qemu- > > > de...@nongnu.org; > > > > > Anthony Liguori; m...@redhat.com > > > > > Subject: Re: [PATCH] xen: make xen-platform a default device > > > > > > > > > > On Thu, 22 May 2014, Gerd Hoffmann wrote: > > > > > > > > Given that libxl always passes -nodefaults to QEMU, this patch > > > > > > > > is > > > going > > > > > > > > to effectively disable xen_platform_pci for all Xen users. It > > > > > > > > is not > a > > > > > > > > good idea. With the patch applied a Xen user would have no way > to > > > > > enable > > > > > > > > xen_platform_pci except for passing some magic command line > > > runes > > > > > via > > > > > > > > device_model_args_hvm. > > > > > > > > > > > > > > In fact this code only runs for "-M xenfv". If you use "-M pc", > > > > > > > the > > > > > > > xen-platform device has to be added manually. Perhaps it would > be > > > > > > > worthwhile to do the opposite, i.e. add the xen-platform device > to "- > > > M > > > > > > > pc" if not using -nodefaults. > > > > > > > > > > > > /me looks at the code. Yes, all the differences between xenfv and > pc > > > > > > machine types are guarded by if (xen_enabled()) these days, > except > > > for > > > > > > adding the platform device. > > > > > > > > > > > > So using the pc machine type should just work on xen, and give you > a > > > > > > machine without the platform device. So it can be added via - > device, at > > > > > > any slot, if needed. No need to patch qemu at all. Adding or not > > > > > > adding xen-platform can easily handled by libxl then, depending on > the > > > > > > xen_platform_pci switch in the config file. > > > > > > > > > > I agree. Changing libxl to always use -M pc and using -device to add > > > > > xen-platform when needed sounds like the best option. > > > > > > > > Really? You opposed this before: > > > > > > > > http://lists.xen.org/archives/html/xen-devel/2013-06/msg01946.html > > > > > > > > stating that you wanted a mechanism to query the running version of > > > QEMU before choosing the machine type. > > > > > > Many QEMU releases have been made since then. I feel more > comfortable > > > with using -M pc, especially given the alternatives that have been > > > proposed. Of course having a mechanism to query the running version of > > > QEMU would still be the safest solution. > > > > But I thought the problem was that, should someone change what 'pc' > means, then libxl would invoke the 'wrong' machine type on a domain > restore. I know that xenfv is essentially 'pc' at the moment but would could > fix on a particular version if compatibility becomes an issue. So, rather than > choosing 'pc' now, should we not choose 'pc-i440fx-1.6' which is the current > default? > > One issue is that -M pc didn't always work with Xen. Now it does and we > are already relying on it in libxl since > 2bc047635b51abd41c917aa2b813211ee0de2c38. It is safe because all QEMU > releases from 1.6 onward work well with Xen and -M pc. Older QEMU > releases are considered ancient and unmaintained. This is what I was > referring to in my last reply. I really meant "we should move away from > xenfv and use a pc.* machine that does not create xen-platform by > default". > > As you say the other issue is the version of the pc machine, especially > in relation to save/restore. However since: > > commit 2bc047635b51abd41c917aa2b813211ee0de2c38 > Author: Anthony PERARD <anthony.per...@citrix.com> > Date: Wed Nov 27 18:21:34 2013 +0000 > > libxl: Handle xen_platform_pci=0 case with qemu-xen. > > we are simply calling QEMU with -M pc if xen_platform_pci=0. I think we > should change that too and backport the patch to 4.4. pc-i440fx-1.6 > seems like a good choice to me.
Yep - that sounds good. Paul
