Re: [PATCH 2 of 8] block: Export I/O topology for block devices and partitions

[Matthew Wilcox <matthew@wil.cx>]

On Thu, Apr 23, 2009 at 12:51:45PM +0200, Jens Axboe wrote:
> > +/**
> > + * blk_queue_alignment - set alignment for the queue
> > + * @q:  the request queue for the device
> > + * @alignment:  alignment offset in bytes
> > + *
> > + * Description:
> > + *   Some devices are naturally misaligned to compensate for things like
> > + *   the legacy DOS partition table 63-sector offset.  Low-level drivers
> > + *   should call this function for devices whose first sector is not
> > + *   naturally aligned.
> > + */
> > +void blk_queue_alignment(struct request_queue *q, unsigned int alignment)
> > +{
> > +	q->alignment = alignment & (q->granularity - 1);
> > +	clear_bit(QUEUE_FLAG_MISALIGNED, &q->queue_flags);
> > +}
> > +EXPORT_SYMBOL(blk_queue_alignment);
> 
> How would low-level drivers know?

ATA reports this in the INQUIRY data.  SCSI reports it in READ CAPACITY 16.

-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."