Re: [Qemu-devel] Are -cdrom/-hda (or -drive if=ide) supposed to work in q35?

[John Snow <jsnow@redhat.com>]

On 06/12/2014 05:03 AM, Markus Armbruster wrote:
> Michael Tokarev <mjt@tls.msk.ru> writes:
>
>> 10.06.2014 10:34, Paolo Bonzini wrote:
>>> Il 10/06/2014 08:30, Michael Tokarev ha scritto:
>>>> Hello.
>>>>
>>>> The question is: are the drive shortcuts - -cdrom, -hda, -hdb etc -
>>>> supposed to work in -machine q35 too?  Or are they merely ignored?
>>>>
>>>>    qemu-system-x86_64 -machine q35 -cdrom foo.img
>> []
>>> It should work.  I remember some complications due to AHCI not
>>> having slaves, but it is a bug.
>> It looks like the "short" -drive if=ide option does not connect the
>> created drive to any bus at all.  With the above command, or with
>> -drive if=ide,index=*,bus=*, info qtree does not show the drive at
>> all.  While -drive if=none,id=X -device ide-cd,drive=X connects the
>> drive to the right bus just fine.
> -drive mixes up configuration of backend and frontend (a.k.a. device
>   model), as follows:
>
> 1. It always defines a backend.  "info block" shows them.
>
> 2. It always defines a few frontend configuration bits for the device
>     models to pick up.
>
> 3. Except with if=none, it posts a request to board code to create a
>     suitable frontend.  It's up to the board code to honor, reject or
>     ignore the request.  The i440FX boards honor it, the Q35 boards
>     ignore it.
>
>     Nobody has gotten around to making the Q35 boards honor it, in part
>     because there has been some confusion on what if=ide is supposed to
>     mean on Q35.  Should it connect an ide-hd / ide-cd in SATA mode or in
>     legacy PATA mode?
>
>     I've always argued for SATA, because for me if=ide does *not* imply a
>     specific kind of HBA any more than if=scsi does, and the "natural"
>     HBA for Q35 is AHCI in SATA mode.
>
>     Kevin (cc'ed) has argued for a way to make it connect in legacy PATA
>     mode.  I'd be fine with that, as long as it's off by default.
>
>     Patches welcome.
>

Kevin, (or anyone else with an opinion for that matter), what is the 
reasoning behind wanting -cdrom to use the old PATA interfaces?

For at least the immediate future, the AHCI device doesn't support the 
mixed-mode SATA/PATA access models, though I suppose we could, it seems 
like a more obvious and simple solution to just allow the shorthand 
syntactic sugar commands to use the native bus of the system until you 
specify otherwise.

I think I will probably begin writing a patch under this assumption 
unless there is a better technical reason not to.

--J