Re: [Qemu-devel] [PATCH 11/35] scsi-disk: support READ DVD STRUCTURE

[Paolo Bonzini <pbonzini@redhat.com>]

On 10/21/2011 01:42 PM, Kevin Wolf wrote:
> There is only one 'goto fail', all other places have a direct return -1.
> It would be good to be consistent.
>
> Also, as this is mostly a refactored copy from the ATAPI code, I wonder
> what our long-term plan is. At which point will we be able to unify what
> we're duplicating right now? Can we share some parts even now?

That's a tricky question.  I think there are three choices:

1) use SCSI as the sole interface exposed by the block layer (with an 
adaptor).  There would be a common implementation of SCSI for 
SCSI-oblivious devices, and other devices (hdev, sg, iscsi) could just 
reason in terms of SCSI.  You could stack the common implementations 
(hard drive and CD-ROM) on top of hdev/iscsi or use passthrough.  This 
however is wrong IMHO because some bits of SCSI code really do deal with 
guest state, for example the tray.

2) let ide-cd create its own SCSI bus and act as an adaptor, similar to 
USB devices.  There would still be duplication for commands that do DMA 
in multiple steps; I think READ CD is the only one.

3) create a separate API just for the purpose of sharing code between 
ATAPI and SCSI (your "can we share some parts even now", basically).


I think I'm leaning towards (3), but I don't think it makes sense to do 
it now unless someone is interested in implementing for example CD 
burning support.  However, I'm leaning towards that also because I 
honestly have no idea how hard (2) would be.

Paolo