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Re: [PATCH v1 16/16] dma-mapping: Disallow .map_sg operations from returning zero on error

On 2021-07-16 07:33, Christoph Hellwig wrote:
On Thu, Jul 15, 2021 at 10:45:44AM -0600, Logan Gunthorpe wrote:
@@ -194,6 +194,8 @@ static int __dma_map_sg_attrs(struct device *dev, struct 
scatterlist *sg,
                ents = ops->map_sg(dev, sg, nents, dir, attrs);
+ WARN_ON_ONCE(ents == 0);

Turns this into a negative error code while we're at it, just to keep
the callers sane?

Right, by this point returning the 0 would pass through dma_map_sg_attrs() OK, but AFAICS dma_map_sgtable() would now get confused and return success but with sgt->nents = 0. Coercing it to an error code (which dma_map_sg_attrs() would then just change right back) seems sensible for the sake of easy robustness.




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