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

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Date:	Mon, 4 Apr 2016 19:47:36 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	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 Mon, Apr 04, 2016 at 06:16:12PM +0100, Al Viro wrote:

> will see NULL map_data; the ->from_user case is sg_start_req() stuff.  IOW,
> SG_IO behaviour for /dev/sg* is different from the generic one...

While we are at it: in bio_map_user_iov() we have
        iov_for_each(iov, i, *iter) { 
                unsigned long uaddr = (unsigned long) iov.iov_base;
                unsigned long len = iov.iov_len;
                unsigned long end = (uaddr + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
                unsigned long start = uaddr >> PAGE_SHIFT;

                /*
                 * Overflow, abort
                 */
                if (end < start)
                        return ERR_PTR(-EINVAL);

                nr_pages += end - start;
                /*
                 * buffer must be aligned to at least hardsector size for now
                 */
                if (uaddr & queue_dma_alignment(q))
                        return ERR_PTR(-EINVAL);
        }

Do we only care about the iov_base alignment?  IOW, shouldn't we check for
iov_len being a multiple of queue_dma_alignment(q) as well?