linux/block
Kiyoshi Ueda 32fab448e5 block: add request update interface
This patch adds blk_update_request(), which updates struct request
with completing its data part, but doesn't complete the struct
request itself.
Though it looks like end_that_request_first() of older kernels,
blk_update_request() should be used only by request stacking drivers.

Request-based dm will use it in bio->bi_end_io callback to update
the original request when a data part of a cloned request completes.
Followings are additional background information of why request-based
dm needs this interface.

  - Request stacking drivers can't use blk_end_request() directly from
    the lower driver's completion context (bio->bi_end_io or rq->end_io),
    because some device drivers (e.g. ide) may try to complete
    their request with queue lock held, and it may cause deadlock.
    See below for detailed description of possible deadlock:
    <http://marc.info/?l=linux-kernel&m=120311479108569&w=2>

  - To solve that, request-based dm offloads the completion of
    cloned struct request to softirq context (i.e. using
    blk_complete_request() from rq->end_io).

  - Though it is possible to use the same solution from bio->bi_end_io,
    it will delay the notification of bio completion to the original
    submitter.  Also, it will cause inefficient partial completion,
    because the lower driver can't perform the cloned request anymore
    and request-based dm needs to requeue and redispatch it to
    the lower driver again later.  That's not good.

  - So request-based dm needs blk_update_request() to perform the bio
    completion in the lower driver's completion context, which is more
    efficient.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
2008-10-09 08:56:18 +02:00
..
Kconfig block: Block layer data integrity support 2008-07-03 13:21:13 +02:00
Kconfig.iosched update I/O sched Kconfig help texts - CFQ is now default, not AS. 2007-02-17 20:08:22 +01:00
Makefile block: unify request timeout handling 2008-10-09 08:56:13 +02:00
as-iosched.c block: make kblockd_schedule_work() take the queue as parameter 2008-10-09 08:56:09 +02:00
blk-barrier.c block: adjust blkdev_issue_discard for swap 2008-10-09 08:56:17 +02:00
blk-core.c block: add request update interface 2008-10-09 08:56:18 +02:00
blk-exec.c Add some block/ source files to the kernel-api docbook. Fix kernel-doc notation in them as needed. Fix changed function parameter names. Fix typos/spellos. In comments, change REQ_SPECIAL to REQ_TYPE_SPECIAL and REQ_BLOCK_PC to REQ_TYPE_BLOCK_PC. 2008-10-09 08:56:03 +02:00
blk-integrity.c block: implement and use {disk|part}_to_dev() 2008-10-09 08:56:07 +02:00
blk-ioc.c cfq-iosched: fix RCU race in the cfq io_context destructor handling 2008-05-07 09:28:57 +02:00
blk-map.c block: make blk_rq_map_user take a NULL user-space buffer 2008-10-09 08:56:11 +02:00
blk-merge.c block: inherit CPU completion on bio->rq and rq->rq merges 2008-10-09 08:56:09 +02:00
blk-settings.c block: unify request timeout handling 2008-10-09 08:56:13 +02:00
blk-softirq.c block: add fault injection mechanism for faking request timeouts 2008-10-09 08:56:17 +02:00
blk-sysfs.c block: add support for IO CPU affinity 2008-10-09 08:56:09 +02:00
blk-tag.c Add some block/ source files to the kernel-api docbook. Fix kernel-doc notation in them as needed. Fix changed function parameter names. Fix typos/spellos. In comments, change REQ_SPECIAL to REQ_TYPE_SPECIAL and REQ_BLOCK_PC to REQ_TYPE_BLOCK_PC. 2008-10-09 08:56:03 +02:00
blk-timeout.c block: use rq complete marking in blk_abort_request() 2008-10-09 08:56:17 +02:00
blk.h block: add fault injection mechanism for faking request timeouts 2008-10-09 08:56:17 +02:00
blktrace.c blktrace: simplify flags handling in __blk_add_trace 2008-10-09 08:56:01 +02:00
bsg.c block: introduce struct rq_map_data to use reserved pages 2008-10-09 08:56:10 +02:00
cfq-iosched.c cfq-iosched: fix queue depth detection 2008-10-09 08:56:09 +02:00
cmd-filter.c block: move holder_dir from disk to part0 2008-10-09 08:56:08 +02:00
compat_ioctl.c Add BLKDISCARD ioctl to allow userspace to discard sectors 2008-10-09 08:56:02 +02:00
deadline-iosched.c deadline-iosched: non-functional fixes 2008-10-09 08:56:03 +02:00
elevator.c block: Add interface to abort queued requests 2008-10-09 08:56:13 +02:00
genhd.c block: add fault injection mechanism for faking request timeouts 2008-10-09 08:56:17 +02:00
ioctl.c block: make partition array dynamic 2008-10-09 08:56:08 +02:00
noop-iosched.c block: let elv_register() return void 2007-12-18 08:29:28 +01:00
scsi_ioctl.c block: introduce struct rq_map_data to use reserved pages 2008-10-09 08:56:10 +02:00