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Re: [Qemu-devel] [PATCH v2] ahci: add -drive support

From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH v2] ahci: add -drive support
Date: Mon, 9 Jul 2012 13:22:09 +0200

On 09.07.2012, at 13:19, Markus Armbruster wrote:

> Alexander Graf <address@hidden> writes:
>> On 09.07.2012, at 13:06, Markus Armbruster wrote:
>>> Kevin Wolf <address@hidden> writes:
>>>> Am 09.07.2012 10:50, schrieb Markus Armbruster:
>>>>> Alexander Graf <address@hidden> writes:
>>>>>> We've had support for creating AHCI devices using -device for a while 
>>>>>> now,
>>>>>> but it's cumbersome to users. We really should provide an easier way for
>>>>>> them to leverage the power of AHCI!
>>>>>> So let's introduce a new if= option to -drive, giving users the same
>>>>>> command line experience as for scsi or ide.
>>>>>> Signed-off-by: Alexander Graf <address@hidden>
>>>>>> ---
>>>>>> v1 -> v2:
>>>>>> - support more than a single drive per adapter
>>>>>> - support index= option
>>>>>> - treat IF_AHCI the same as IF_IDE
>>>>> Inhowfar?  Not obvious to me from the patch, or the diff patch v1.
>>>>>> - add is_ata() helper to match AHCI || IDE
>>>>> Not addressed:
>>>>> Once we switch to q35, if=ahci will become a redundant wart: to add
>>>>> drives to the board's AHCI controller, you'll have to use if=ide.
>>>>> if=ahci will create new controllers, which is generally not what you
>>>>> want.  Ugh.
>>>> Can we even make it the default with q35 as long as our AHCI controller
>>>> doesn't also expose a legacy interface for compatibility?
>>> Err, what else could we do with if=ide with q35?
>> We could create a cmd646 and attach drives to that.
> Naive use of the command line then connects your drives to some an old
> and slow add-on controller instead of the perfectly servicable and fast
> on-board controller.
> Let me rephrase my question: s/could/should/

Well, what I'm saying is that we should distinguish between -hda and if=ide. 
Make -hda attach the disk to the default controller. Make -cdrom attach the 
cdrom to the default controller. Make if=ide attach the disk to an IDE 
controller. If there's none in the system, spawn one.

That way the "naive" use case of passing no -hda or -hda -hdb is guaranteed to 
be good and fast. The case where a user actually asks for an IDE device, he 
still gets what he asked for.


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