[PATCH] crypto: scatterwalk_copychunks() fails to advance through scatterlist

[Herbert Xu]

On Mon, Mar 19, 2007 at 07:55:08PM -0400, J. Bruce Fields wrote:
> In the loop in scatterwalk_copychunks(), if walk->offset is zero,
> then scatterwalk_pagedone rounds that up to the nearest page boundary:
> 
> 		walk->offset += PAGE_SIZE - 1;
> 		walk->offset &= PAGE_MASK;
> 
> which is a no-op in this case, so we don't advance to the next element
> of the scatterlist array:
> 
> 		if (walk->offset >= walk->sg->offset + walk->sg->length)
> 			scatterwalk_start(walk, sg_next(walk->sg));
> 
> and we end up copying the same data twice.

Thanks for the patch.  However I still have a question as to why
this is happening.

As far as I can see scatterwalk_copychunks is only called in two
places.  In both spots it only processes one block of data.  Since
we set the maximum block size to PAGE_SIZE/8 I don't see how you
can get an offset of zero and still roll over to the next page
in scatterwalk_copychunks.

So perhaps the bug is elsewhere in the original patch?

Your patch looks like a good clean-up anyway but I just wanted to
make sure that I understand what the problem is first.

Cheers,
-- 
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