Re: [Qemu-devel] Question about xen disk unplug support for ahci missed in qemu

[Fabio Fantoni <fabio.fantoni@m2r.biz>]

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2015-10-19 18:57 GMT+02:00 Stefano Stabellini <
stefano.stabellini@eu.citrix.com>:

> On Mon, 19 Oct 2015, John Snow wrote:
> > On 10/19/2015 07:44 AM, Stefano Stabellini wrote:
> > > On Mon, 19 Oct 2015, Gerd Hoffmann wrote:
> > >>   Hi,
> > >>
> > >>>> I'm trying to follow this discussion as best as I am able, but my
> lack
> > >>>> of experience with Xen prevents me from really participating in a
> > >>>> meaningful way.
> > >>>>
> > >>>> (I see that Laszlo is still discussing some CD-ROM issues with Fabio
> > >>>> which may be of interest to me...)
> > >>>>
> > >>>> At any rate, I won't be authoring any Xen-specific hacks to the AHCI
> > >>>> device, but I do have plans to implement hot-plugging emulation as
> per
> > >>>> the AHCI spec. Perhaps this is sufficient for the Xen layer, but
> someone
> > >>>> else will need to author the appropriate glue code.
> > >>>>
> > >>>> If "real" hot-plugging is not sufficient, we'll need to discuss
> further,
> > >>>> preferably over some RFC patches.
> > >>>
> > >>> That's fine. AHCI hot-plugging would go a long way and once we have
> > >>> that, the rest is easy.
> > >>
> > >> Can we get some more background on this?
> > >>
> > >> IIRC the IDE bits are needed to boot hvm guests, which goes like this:
> > >>
> > >>   (1) boot disk is hooked up using both xenbus and ide.
> > >>   (2) seabios boots using ide.
> > >>   (3) linux kernel activates xenbus, at which point qemu zaps the ide
> > >>       disks to avoid the disk being present twice in the system.
> > >>
> > >> Correct?
> > >>
> > >> Do we really want repeat this exercise for AHCI?  Alot has changed
> since
> > >> this boot hack for ide was added ...
> > >>
> > >> As far I know OVMF has xenbus drivers, so OVMF should already boot xen
> > >> guests just fine without this, correct?
> > >
> > > I agree with you that the current unplug in nasty. Also I don't care
> > > much about AHCI, in fact I don't think we should be spending efforts
> > > into making that scenario work better. I think we should be working on
> > > OVMF instead and fix the bug about empty cdrom drives reported by
> Fabio.
> > >
> >
> > OVMF and AHCI go hand in hand here from my viewpoint. I'm happy to debug
> > any OVMF+SATA/AHCI problems that are reported.
> >
> > Last I saw, Laszlo asked Fabio for some more information on this
> > problem, so I am waiting for that information to start work on that
> issue.
>
> Fabio reported a bug using OVFM+xen_disk, no AHCI involved. OVFM has
> already support for the Xen PV disk protocol, see
> OvmfPkg/XenPvBlkDxe/XenPvBlkDxe.c.
>

I not tried with ahci in ovmf in latest because as you told that is a
missing unplug case in qemu.

I tried with xendisk and ide, the empty cdrom problem is with both, from xl
domU cfg:

',raw,xvdb,ro,cdrom' for xendisk and ',raw,hdb,ro,cdrom' for ide.

Using seabios instead boot correctly, with ovmf not:
http://lists.xen.org/archives/html/xen-devel/2015-10/msg01833.html

If I remember good also in latest test persist also the problem that
ovmf not respect the boot order parameter.

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