On Thu, May 07 2009, Boaz Harrosh wrote: > > Osd library needs to submit pre-allocated bios, form several sources. > osdblk exofs and pNFS-layout driver all have prepared bios for IO submission. > On top of that the osd library needs to append additional segments to the > IO memory, for get/set attributes and more. > > All these are done today by use of a temporary hack - blk_rq_append_bio. > This is bad on few accounts. > 1. blk_rq_append_bio was not meant to be exported and is very specific to its users. > 2. blk_rq_append_bio does not support chained bios. > 3. blk_rq_append_bio does not bounce the bio and therefore current osd implementation > has a bug. > > The proposed solution adds two new fixtures to the block layer, and a corresponding > fixing patch to osd. These are: > > [PATCH 1/4] allow blk_rq_map_kern to append to requests > [PATCH 2/4] libosd: Use new blk_rq_map_kern > > This is originally a James patch and it's used, to let blk_rq_map_kern append it's buffer > to existing bio, and there for is able to be called multiple times in a loop, to append > multiple segments. This API can also be useful for scsi/block targets that have segment > information in some other memory structure (like scatterlist) and wants to set it into > a request. Until such time that they have a proper support for mapping scatterlists directly. > (Since above called on long lists might not be good for performance) > > Here in osd it makes tons of sense, and should be considered for inclusion. > (The patches are based on linus-tip but should patch on block tree) > > [RFC 3/4] New blk_make_request(), takes bio, returns a request > [RFC 4/4] libosd: Use of new blk_make_request > > Here I propose a new block API, that will support proper delegation of a bio > to a full request. Please read inside the patch descriptions for details. > After this patch both osd and block layer will have the proper support for osdblk > driver as well as future needs. > These patches also eliminate the last use of blk_rq_append_bio which can be now un-exported. > > These two patches conflic with Tejun's branch and are based on linus-tip. Upon positive review > I will serialize them with Tejun and submit them properly. But first they must be agreed upon. > Jens, I specially need your opinion on this? Looks sane to me. Can you resubmit against 'for-2.6.31' of the block git repo? -- Jens Axboe -- 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
