On 2018-09-21 10:48 AM, Bjorn Helgaas wrote: >> I think the use of "map" in this context is slightly confusing because the >> general expectation is that map/unmap must be balanced. Yeah, Jason said the same thing, but having an empty unmap function seems wasteful and Christoph said to just remove it. My opinion is that it's not that big an issue one way or another -- if we have to add an unmap later it's not really that hard. >> If you keep "map", maybe add a sentence or two about why there's no >> corresponding unmap? Will do. > Another wrinkle is that "map" usually takes an A and gives you back a > B. Now the caller has both A and B and both are still valid. > Here we pass in an SGL and the SGL is transformed, so the caller only > has B and A has been destroyed, i.e., the SGL can no longer be used as > it was before, and there's no way to get A back. I wouldn't say that. Our map_sg function is doing the same thing dma_map_sg is: it sets the DMA address and length in the scatter list. So B is still A just with other fields set. If the caller wanted to map this SG in a different way they can still do so and the new DMA address/length would override the old values. (Normally, you'd want to unmap before doing something like that, but seeing our unmap is an empty operation, we wouldn't have to do that.) Logan
