From 32fab448e5e86694beade415e750363538ea5f49 Mon Sep 17 00:00:00 2001 From: Kiyoshi Ueda Date: Thu, 18 Sep 2008 10:45:09 -0400 Subject: [PATCH] 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: - 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 Signed-off-by: Jun'ichi Nomura Signed-off-by: Jens Axboe --- block/blk-core.c | 57 +++++++++++++++++++++++++++++++++++------- include/linux/blkdev.h | 2 ++ 2 files changed, 50 insertions(+), 9 deletions(-) diff --git a/block/blk-core.c b/block/blk-core.c index 37fba001bdcf..527d43e982bb 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -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 diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index e23b838825bd..e82a84c9f37a 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -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. -- 2.20.1