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

[John Snow <jsnow@redhat.com>]

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.

Thanks,
--js