On Thu, 9 Oct 2008 11:08:37 -0700 Seokmann Ju <seokmann.ju@xxxxxxxxxx> wrote: > I've got a quick question on the blk_rq_map_sg() API usage. > In an efforts of implementing pass through support on FC transport > layer, the transport would call blk_rq_map_sg() API to map the pages > in the bio structure so that the LLD could DMA to/from the mapped > addresses - as specified in the section 2.2 of the ~/Documentation/ > block/biodoc.txt. > To me, it seems like a right way to do..., could anyone comment on > this approach? Sounds reasonable for me. fc transport calls blk_rq_map_sg() and then llds easily call dma_map_sg and do DMA transfer. > Also, I couldn't find symmetric counter-part for the API (i.e., > blk_rq_unmap_sg() or similar). > Does this means that we don't need to unmap those addresses? There is no symmetric counterpart for blk_rq_unmap_sg. All you need to do is to free scatter lists. dma_map_sg maps addresses in scatter lists to DMA-capable addresses. So you need to call its symmetric counterpart, dma_unmap_sg after the completion of DMA transfer. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
