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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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

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