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Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD (drivers/block/skd*)

From Christoph Hellwig <hch@infradead.org>
Newsgroups linux.kernel
Subject Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD (drivers/block/skd*)
Date 2016-04-07 18:00 +0200
Message-ID <rlkvE-692-7@gated-at.bofh.it> (permalink)
References (1 earlier) <rk6Eq-7Fc-17@gated-at.bofh.it> <rkgks-6rb-35@gated-at.bofh.it> <rkhJv-7va-7@gated-at.bofh.it> <rkiPf-8d0-1@gated-at.bofh.it> <rkmpP-2lv-13@gated-at.bofh.it>
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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?

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[RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD  (drivers/block/skd*) Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-04 05:40 +0200
  Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD  (drivers/block/skd*) Christoph Hellwig <hch@infradead.org> - 2016-04-04 09:00 +0200
    Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD  (drivers/block/skd*) Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-04 19:20 +0200
      Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD  (drivers/block/skd*) Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-04 20:50 +0200
        Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD  (drivers/block/skd*) Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-04 22:00 +0200
          Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD  (drivers/block/skd*) Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-05 01:50 +0200
            Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD  (drivers/block/skd*) Christoph Hellwig <hch@infradead.org> - 2016-04-07 18:00 +0200
              Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD  (drivers/block/skd*) Al Viro <viro@ZenIV.linux.org.uk> - 2016-04-08 21:30 +0200
      Re: [RFC] weird semantics of SG_DXFER_TO_FROM_DEV in BLK_DEV_SKD  (drivers/block/skd*) Christoph Hellwig <hch@infradead.org> - 2016-04-07 18:00 +0200

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