linux-kernel - Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV

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Date:	Thu, 7 Apr 2016 08:55:33 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Christoph Hellwig <hch@...radead.org>, Jens Axboe <axboe@...com>,
	linux-kernel@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD
 (drivers/block/skd*)

On Tue, Apr 05, 2016 at 12:45:08AM +0100, Al Viro wrote:
> AFAICS, what we need there is simply
> 	nr_pages = iov_iter_npages(iter);
> 	alignment = iov_iter_alignment(iter);
> 	if (alignment & (queue_dma_alignment(q) | q->dma_pad_mask))
> 		copy = true;
> and I really wonder if we care about special-casing the situation when the
> ends are not aligned to queue_virt_boundary(q).  If we don't, we might as
> well add queue_virt_boundary(q) to the mask we are checking.  If we do,
> it's not hard to add a variant that would calculate both the alignment and
> alignment for internal boundaries...

I suspect this is the right thing to do.  Care to send a patch to Jens?