Re: [PATCH] block: add protocol discriminators to requests and queues

[James Bottomley <James.Bottomley@SteelEye.com>]

On Thu, 2007-08-02 at 12:51 -0600, Matthew Wilcox wrote:
> On Thu, Aug 02, 2007 at 12:47:25PM -0500, James Bottomley wrote:
> > This looks small and innocuous, but it's actually the beginning of
> > moving the upper layer drivers into block and adding a filtering layer.
> > The idea is that the queue contains a queue_protocol parameter which
> > details what the device actually speaks.  The requests are likewise
> > filled in with a cmd_protocol parameter by the ULDs (or bsg if it's a
> > user initiated command, using the existing sgv4 protocol fields).
> > 
> > Now we have the capability of adding say native ATA pass through to BSG,
> > but also we can add things like an ATAPI filter:  sr creates SCSI
> > requests, but these could be sent through a PACKET_COMMAND wrapper and
> > emerge as BLK_PROTOCOL_ATAPI before being sent to the device.  Likewise,
> > sd requests going to BLK_PROTOCOL_ATA devices would have to go through
> > SATL filters.  
> 
> Will it also add the ability to add device-specific filters?  For
> example, the CD burners that have manufacturer specific opcodes to turn
> on various features that are safe for users to use ... but have to be
> limited to root-only currently as we can't know what kind of device the
> command is going to.

I wasn't planning on doing this ... the idea is basically a protocol
conversion filter.  Device quirks don't quite fit into this model.

James