Re: [PATCH 4/4] nvmet-fc: Use new SGL alloc/free helper for requests

Christoph Hellwig
2018-03-29T18:15:50Z

On Thu, Mar 29, 2018 at 11:02:10AM -0600, Logan Gunthorpe wrote:
> Per the bug in the previous patch, I don't think that was ever a valid
> assumption. It doesn't have anything to do with the sgl_alloc change
> either. The dma_map interface is allowed to merge SGLs and that's why it
> can return fewer nents than it was passed. I'm not sure how many or
> which DMA ops actually do this which is why it hasn't actually
> manifested itself as a bug; but it is part of how the interface is
> specified to work.

Most iommus can, it just is very unlikely do happen in block drivers
given that the block layer already merges segments higher up.