On Fri, 07 Mar 2008 09:07:23 +0900 Tejun Heo <htejun@xxxxxxxxx> wrote: > Jens Axboe wrote: > >>> If we want the use paradigm shared between block and driver, then I > >>> think the best approach is to keep all the bios the same (so not adjust > >>> for padding), but do adjust in the blk_rq_map_sg(). That way we have > >>> the padding and draining unwind information by comparing with the bio. > >> Adjusting only sg in blk_rq_map_sg (like drain) looks much > >> better. This works with libata for me. > > > > Looks like a much better solution to me. Anyone have any valid > > objections against moving the padding to the sg map time? > > Not necessarily objections but some concerns. > > * As completion is done in bio terms, it makes completion from LLDs a > bit cumbersome, but this is unavoidable if we break sum(bio) == sum(sg). What do you mean? How does sub(bio) affect LLDs? > * I've been wondering why we are not using sg chain / table or whatever > directly in bios and maybe rq_map_sg can go away in future. You mean that LLDs use bios directly? For me, sg and bio have very different objectives and it's a clean layer separation. > How about separating out the padding / draining adjustment into a > separate interface? Say, blk_rq_apply_extra() and blk_rq_undo_extra() > and make it the responsibility of the LLD which requested > padding/draining to apply and undo the adjustments? It can undo the > adjustments when it returns the the request to its upper layer. If rq > completion is handled by upper layer, it will do the right thing. If rq > completion is handled by LLD, it can see the bio it wants to see. If possible, I'd like to avoid creating APIs for them. I think that the current approach is much better than such APIs. -- 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
