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Date: Wed, 1 Apr 2009 22:44:15 +0900 From: Tejun Heo <tj@...nel.org> To: axboe@...nel.dk, bharrosh@...asas.com, linux-kernel@...r.kernel.org, fujita.tomonori@....ntt.co.jp Subject: [RFC PATCHSET block] block: blk-map updates and API cleanup Hello, all. These patches are available in the following git tree but it's on top of the previous blk-map-related-fixes patchset which needs some updating, so this posting is just for review and comments. This patchset needs to spend quite some time in RCs even if it gets acked eventually, so definitely no .30 material. Please also note that I haven't updated the comment about bio chaining violating queue limit, so please ignore that part. git://git.kernel.org/pub/scm/linux/kernel/git/tj/misc.git blk-map http://git.kernel.org/?p=linux/kernel/git/tj/misc.git;a=shortlog;h=blk-map The goals of this patchset are * Clean up and refactor blk/bio PC map API interface and implementation. * Add blk_rq_map_kern_sg() so that in-kernel user can issue multi-segment PC request. scsi_lib.c currently does this directly by building rq itself. * This is also in the general direction of making block layer interface more strictk. For PC requests, users only get to deal with requests and buffers. This patchset uses sg list to pass multi-segment memory area into blk_rq_map_kern_sg() and also uses sgl to simplify internal implementation. Boaz Harrosh has some objections against both of them. For the former, I can't really think of using anything other than sgl for the API. For the second point, the use of sgl inside bio for map implementation does add overhead for blk_rq_map_user*() calls because it first maps to sgl and then gets interpreted to bvec. The reason that sgl is used for implementation is because it has richer API, mainly sg_mapping_iter. So, it basically comes down to whether reducing the overhead of alloc/copying and freeing sgl one more time for each SG_IO call is worth the added complexity. I don't really think it will show up anywhere but if this is a problem, switching over to bvec for internal implementation wouldn't be too difficult although then copying back and forth would require some hairy code. Also, please note that the new code is more generic in that it can handle highpage io and bouncing buffers without adding any special provision for them. I think the root problem is that we really don't have a proper data structure and API for handling in-kernel segments. iovec can't cover high pages. sgl is currently the closest thing but it's fat due for the dma mapping addresses. I think what we need to do is improve sgl (sgt) such that it maintains separate lists for kernel segments and DMA mappings and enable it to be linked, spliced, cloned or whatever, so we don't have to re-map back and forth. Well, that's for another time. This patchset contains the following 17 patches. 0001-blk-map-move-blk_rq_map_user-below-blk_rq_map_use.patch 0002-scatterlist-improve-atomic-mapping-handling-in-mapp.patch 0003-blk-map-improve-alignment-checking-for-blk_rq_map_u.patch 0004-bio-bio.h-cleanup.patch 0005-bio-cleanup-rw-usage.patch 0006-blk-map-bio-use-struct-iovec-instead-of-sg_iovec.patch 0007-blk-map-bio-rename-stuff.patch 0008-bio-reimplement-bio_copy_user_iov.patch 0009-bio-collapse-__bio_map_user_iov-__bio_unmap_user.patch 0010-bio-use-bio_create_from_sgl-in-bio_map_user_iov.patch 0011-bio-add-sgl-source-support-to-bci-and-implement-bio.patch 0012-bio-implement-bio_-map-copy-_kern_sgl.patch 0013-blk-map-implement-blk_rq_map_kern_sgl.patch 0014-scsi-replace-custom-rq-mapping-with-blk_rq_map_kern.patch 0015-bio-blk-map-kill-unused-stuff-and-un-export-interna.patch 0016-blk-map-bio-remove-superflous-len-parameter-from-b.patch 0017-blk-map-bio-remove-superflous-q-from-blk_rq_map_-u.patch 0001 is misc prep. 0002 improves sg_miter so that it can be used for copying between sgls. 0003 update alignment checking during direct mapping (I think this is correct because there's no other way for low level drivers to express segment length requirement). 0004-0007 cleans up the code for future updates. 0008-0013 refactors map code and adds blk_rq_map_kern_sgl(). 0014 drops custom sg mapping in scsi_lib.c and make it use blk_rq_map_kern_sgl(). 0015 kills now unused stuff including blk_rq_append_bio(). 0016-0017 removes duplicate parameters from API. This patchset is on top of the current linux-2.6-block#for-linus[1] + blk-map-related-fixes patchset[2]. block/blk-map.c | 216 ++---- block/bsg.c | 5 block/scsi_ioctl.c | 21 drivers/block/pktcdvd.c | 2 drivers/cdrom/cdrom.c | 2 drivers/mmc/host/sdhci.c | 4 drivers/scsi/device_handler/scsi_dh_alua.c | 2 drivers/scsi/device_handler/scsi_dh_emc.c | 2 drivers/scsi/device_handler/scsi_dh_rdac.c | 2 drivers/scsi/scsi_lib.c | 113 --- drivers/scsi/scsi_tgt_lib.c | 3 drivers/scsi/sg.c | 8 drivers/scsi/st.c | 3 fs/bio.c | 980 +++++++++++++++-------------- include/linux/bio.h | 170 ++--- include/linux/blkdev.h | 23 include/linux/scatterlist.h | 11 lib/scatterlist.c | 49 + 18 files changed, 806 insertions(+), 810 deletions(-) Thanks. -- tejun [1] 714ed0cf62319b14dc327273a7339a9a199fe046 [2] http://thread.gmane.org/gmane.linux.kernel/815647 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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