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Date: Tue, 29 Sep 2009 15:55:39 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
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Subject: [Qemu-devel] Re: [PATCH 0/2] fix virtio_blk serial pci config
	breakage
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To: john cooper <john.cooper@third-harmonic.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>, john cooper <john.cooper@redhat.com>, Rusty Russell <rusty@rustcorp.com.au>, qemu-devel@nongnu.org, Avi Kivity <avi@redhat.com>, jens.axboe@oracle.com, Vadim Rozenfeld <vrozenfe@redhat.com>

john cooper wrote:
> Anthony Liguori wrote:
>
>> 2) Passing an ATA identity page is goofy.  We should just pass the 
>> serial number and let Linux generate the identity page.
>
> I have a hard time disagreeing with that comment.
>
> But the rationale that got us here was from the
> user's perspective this information could be
> trivially exposed via a preexisting interface vs.
> creating a new interface as I'd done initially.
> It was also pointed out other defined fields in
> the identify page exist which were potentially
> useful.  So pressing a HDIO_GET_IDENTITY ioctl
> into service here didn't seem unreasonable.

virtio-blk isn't an ATA device so why pretend like it is?

We can present the information we think is useful to the guest in a 
concise format and then if the guest wants to pretend it's an ATA 
device, it can create the ATA identify page on the fly.

>> Just because Linux requires this as it's user space interface, that 
>> doesn't mean that other guests will (like Windows).  Instead of 
>> exposing an opaque blob, we should expose the information we need in 
>> a structured way.
>
> The identify page is defined as the return of an
> "identify drive" command from an ATA drive/controller.
> I'd hazard it is a familiar structure in a windows
> driver/userland context as well.

Regards,

Anthony Liguori