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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 19 Oct 2015, Fabio Fantoni wrote:
> Il 19/10/2015 12:18, Stefano Stabellini ha scritto:
> > On Fri, 16 Oct 2015, John Snow wrote:
> > > On 10/13/2015 01:10 PM, Stefano Stabellini wrote:
> > > > On Tue, 13 Oct 2015, John Snow wrote:
> > > > > On 10/13/2015 11:55 AM, Fabio Fantoni wrote:
> > > > > > I added ahci disk support in libxl and using it for week seems that
> > > > > > was
> > > > > > ok, after a reply of Stefano Stabellini seems that xen disk unplug
> > > > > > support only ide disks:
> > > > > > http://git.qemu.org/?p=qemu.git;a=commitdiff;h=679f4f8b178e7c66fbc2f39c905374ee8663d5d8
> > > > > > 
> > > > > > Today Paul Durrant told me that even if pv disk is ok also with ahci
> > > > > > and
> > > > > > the emulated one is offline can be a risk:
> > > > > > http://lists.xenproject.org/archives/html/win-pv-devel/2015-10/msg00021.html
> > > > > > 
> > > > > > 
> > > > > > I tried to take a fast look in qemu code but I not understand the
> > > > > > needed
> > > > > > thing for add the xen disk unplug support also for ahci, can someone
> > > > > > do
> > > > > > it or tell me useful information for do it please?
> > > > > > 
> > > > > > Thanks for any reply and sorry for my bad english.
> > > > > > 
> > > > > I'm not entirely sure what features you need AHCI to support in order
> > > > > for Xen to be happy.
> > > > > 
> > > > > I'd guess hotplugging, but where I get confused is that IDE disks
> > > > > don't
> > > > > support hotplugging either, so I guess I'm not sure sure what you
> > > > > need.
> > > > > 
> > > > > Stefano, can you help bridge my Xen knowledge gap?
> > > >   Hi John,
> > > > 
> > > > we need something like hw/i386/xen/xen_platform.c:unplug_disks but that
> > > > can unplug AHCI disk. And by unplug, I mean "make disappear" like
> > > > pci_piix3_xen_ide_unplug does for ide.
> > > > 
> > > 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.
> > 
> > Thanks,
> > 
> > Stefano
> 
> Thanks for any improvement you will do.
> About AHCI hotplugging will remove bad thing of actual "xen unplug" in
> seabios/ovmf but not the hybrid pv solution right?

Yeah, it would still be an hybrid solution


> Doing without hybrid like what I tried you told me with ovmf probably is
> better solution after solving other bugs but probably someone don't want plain
> remove it.

Yes, I think OVMF with PV disks is a better approach and we'll fix any
bugs you find. If you find other bugs, send them to the list!


> About empty cdrom not working in ovmf but needed by xl cd-insert/cd-eject I
> suppose that is easly reproducible, I had it in any case I tested.
> If not and more details are needed tell me and I'll rebuild and test following
> Lazslo instructions.
 
No worries, we should be able to repro and fix it, thanks for the
report!

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