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, 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.


> Can we just have xenbus drivers for seabios too?  seabios can run disk
> drivers in 32bit mode meanwhile, so this should not be as difficult any
> more as it used to be.

Sure, I would be happy to see that happen, but I won't be working on it.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel