Re: Re: Unaligned scatter-gather buffers and usb-storage

[Jens Axboe <axboe@suse.de>]

On Wed, Nov 19 2003, James Bottomley wrote:
> On Wed, 2003-11-19 at 07:04, Jens Axboe wrote:
> > On Wed, Nov 19 2003, Oliver Neukum wrote:
> > > 
> > > > > You could add a scsi_host fields or bits specifying alignment
> > > > > restrictions, and enforce them as needed in upper level drivers.
> > > > 
> > > > The queue already has such a restriction embedded, see bio_map_user()
> > > > and queue_dma_alignment().
> > > 
> > > Very well, as far as sd and sr are concerned, but it doesn't help for
> > > sg and st, does it?
> > 
> > They both have a queue through the scsi device structure. But you could
> > put the value someplace else if you wanted.
> 
> Actually, the sg case should be fine, because it shares the queue with
> the other attachment (unless it's a processor or other unrecognised
> device).
> 
> but, regardless, the queue is already set up (for all devices, including
> st) in either slave_alloc, or slave_configure, so you could call the
> alignment setting routine there.

That was my point, yes.

> Alternatively, we could add this as yet another parameter to the host
> and template structures.  Any preferences?

I suppose you have to, if you want LLD to be able to pass it down.

-- 
Jens Axboe



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