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



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? 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.

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.

Thanks for any reply and sorry for my bad english.

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