Re: [PATCH 1/4] virtio_blk: deprecate the 1024-byte ID field.

john cooper
2009-10-05T16:28:31Z

Christian Borntraeger wrote:
> Am Dienstag 29 September 2009 19:18:09 schrieb Rusty Russell:
>> PCI, lguest and s390 can all only support 256-byte configuration
>> space. So, this giant field broke just about everyone.
>> Unfortunately, removing it is not so simple: we don't want to break
>> old userspace, but we're going to want to re-use that part of the
>> struct.
>>
>> So, modern users can #define VIRTIO_BLK_IDENTIFY_DEPRECATED to indicate
>> that they know it's no longer in the config struct, and can use any
>> new features (all new features which add a configuration field will
>> conflict with this deprecated one).
>
>
> Since s390 never used the giant id field, it would be ok for us just delete it
> (without the #define). IIRC kvm-userspace also never used that. Since qemu
> upstream seems to use that field your way seems to be the only compatible...

It seems simply retiring use of the VIRTIO_BLK_F_IDENTIFY
binary value should be sufficient. The patch which
implemented the cooperating logic in qemu was dropped
due to the config space issue. So the case of a virtio_blk
driver successfully negotiating the feature and trying to
access the now depreciated structure area should effectively
be a non-issue. The bit value can be reclaimed for reuse
in the future when concern over any suspected usage falls
into the noise.

-john

--
john.cooper@redhat.com