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

[Kevin Wolf <kwolf@redhat.com>]

[ CC qemu-block ]

Am 13.10.2015 um 19:10 hat Stefano Stabellini geschrieben:
> 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.

Maybe this would be the right time to stop the craziness with your
hybrid IDE/xendisk setup. It's a horrible thing that would never happen
on real hardware.

Can't you just teach SeaBIOS how to deal with your PV disks and then
only add that to your VM and forget about IDE/AHCI? I mean, that's how
it's done for virtio-blk, and it doesn't involve any insanities like
ripping out non-hotpluggable devices.

Hm... How does a reboot of a machine that had its IDE already removed
actually work? Do you restart the qemu process on reboot?

Kevin