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block: add request update interface

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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>
This commit is contained in:
Kiyoshi Ueda 2008-09-18 10:45:09 -04:00 committed by Jens Axboe
parent e3335de940
commit 32fab448e5
2 changed files with 50 additions and 9 deletions
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57
block/blk-core.c
View file

@ -1806,6 +1806,22 @@ void end_request(struct request *req, int uptodate)
}
EXPORT_SYMBOL(end_request);
static int end_that_request_data(struct request *rq, int error,
unsigned int nr_bytes, unsigned int bidi_bytes)
{
if (rq->bio) {
if (__end_that_request_first(rq, error, nr_bytes))
return 1;
/* Bidi request must be completed as a whole */
if (blk_bidi_rq(rq) &&
__end_that_request_first(rq->next_rq, error, bidi_bytes))
return 1;
}
return 0;
}
/**
* blk_end_io - Generic end_io function to complete a request.
* @rq: the request being processed
@ -1832,15 +1848,8 @@ static int blk_end_io(struct request *rq, int error, unsigned int nr_bytes,
struct request_queue *q = rq->q;
unsigned long flags = 0UL;
if (rq->bio) {
if (__end_that_request_first(rq, error, nr_bytes))
return 1;
/* Bidi request must be completed as a whole */
if (blk_bidi_rq(rq) &&
__end_that_request_first(rq->next_rq, error, bidi_bytes))
return 1;
}
if (end_that_request_data(rq, error, nr_bytes, bidi_bytes))
return 1;
/* Special feature for tricky drivers */
if (drv_callback && drv_callback(rq))
@ -1922,6 +1931,36 @@ int blk_end_bidi_request(struct request *rq, int error, unsigned int nr_bytes,
}
EXPORT_SYMBOL_GPL(blk_end_bidi_request);
/**
* blk_update_request - Special helper function for request stacking drivers
* @rq: the request being processed
* @error: %0 for success, < %0 for error
* @nr_bytes: number of bytes to complete @rq
*
* Description:
* Ends I/O on a number of bytes attached to @rq, but doesn't complete
* the request structure even if @rq doesn't have leftover.
* If @rq has leftover, sets it up for the next range of segments.
*
* This special helper function is only for request stacking drivers
* (e.g. request-based dm) so that they can handle partial completion.
* Actual device drivers should use blk_end_request instead.
*/
void blk_update_request(struct request *rq, int error, unsigned int nr_bytes)
{
if (!end_that_request_data(rq, error, nr_bytes, 0)) {
/*
* These members are not updated in end_that_request_data()
* when all bios are completed.
* Update them so that the request stacking driver can find
* how many bytes remain in the request later.
*/
rq->nr_sectors = rq->hard_nr_sectors = 0;
rq->current_nr_sectors = rq->hard_cur_sectors = 0;
}
}
EXPORT_SYMBOL_GPL(blk_update_request);
/**
* blk_end_request_callback - Special helper function for tricky drivers
* @rq: the request being processed

2
include/linux/blkdev.h
View file

@ -791,6 +791,8 @@ extern void blk_complete_request(struct request *);
extern void __blk_complete_request(struct request *);
extern void blk_abort_request(struct request *);
extern void blk_abort_queue(struct request_queue *);
extern void blk_update_request(struct request *rq, int error,
unsigned int nr_bytes);
/*
* blk_end_request() takes bytes instead of sectors as a complete size.