Re: [Xen-devel] [PATCH v2][RFC] libxl: Add AHCI support for upstream qemu

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Tue, 19 May 2015, Fabio Fantoni wrote:
> Il 19/05/2015 12:40, Wei Liu ha scritto:
> > On Mon, May 18, 2015 at 07:22:01PM +0200, Fabio Fantoni wrote:
> > > Il 18/05/2015 17:53, Wei Liu ha scritto:
> > > > On Thu, May 14, 2015 at 01:11:13PM +0200, Fabio Fantoni wrote:
> > > > > Usage:
> > > > > ahci=0|1 (default=0)
> > > > > 
> > > > > If enabled adds ich9 disk controller in ahci mode and uses it with
> > > > > upstream qemu to emulate disks instead of ide.
> > > > Is ICH9 available in our default setup?
> > > > 
> > > > Why do we not always enable AHCI?
> > > ahci seems require ich9 controller (default in q35 but not in older used
> > > by
> > > xen), I think that change it ide->ahci automatically for all cases may
> > > causes problems, probably in save/restore and more probably in windows <=7
> > > without pv where change ide<->ahci require a registry change for not have
> > > blue screen.
> > > 
> > I guess we now have a QEMU with Q35. But migrating from previous
> > previous versions will indeed need to be taken care of.
> 
> This patch don't add q35 cipset support but only ich9 ahci disk controller in
> older and only cipset supported in xen.

This is pretty nice actually, thanks for the patch!


> Time ago I tried to add q35 support in xen but I had some problems I was
> unable to solves and nobody helped me.
> Q35 have newer ich9 ahci disk controller as default, on older cipset must be
> added (done in this patch).
> qemu, kvm ovmf already support q35, xen need changes at least in hvmloader
> (that I'm probably unable to do) and libxl (that I started time ago without
> good result), Add ahci support and switch all qemu parameters in libxl to new
> -device is a good start also for future q35 support (are both part needed
> based on my old q35 tests on xen)

Yeah, going q35 opens a whole new can of worms. I think that adding the
ich9 chipset to the existing machine is a good compromise.


> > 
> > > > > It doesn't support cdroms which still use ide (cdroms will use
> > > > > "-device
> > > > > ide-cd" as new qemu parameters)
> > > > > Ahci requires new qemu parameters but for now other emulated disks
> > > > > cases
> > > > > remains with old ones because automatic bus selection seems bugged in
> > > > > qemu using new parameters. (I'll retry)
> > > > > 
> > > > Buggy as in? Have you reported to QEMU upstream?
> > > Already reported long time ago in xen-devel and qemu-devel, the only reply
> > > from qemu-devel was to use fixed bus and is what I did in v2 of this
> > > patch.
> > > Can someone tell me if can be a problem fixed bus?
> > > 
> > I don't have enough knowledge on this. Maybe Anthony and Stefano have
> > more insight.

Let me get this straight: cdrom still works but goes via ide. In
addition AHCI disks can be attached. Seems good to me.

Have you tested Windows?

If this works with Windows too, I would expose an ahci option
(default=off) in the config file. If ahci=on, then all disks could be
exposed via ahci. Does this seem sensible? In a couple of releases, if
it works well, we could make ahci=on the default.

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