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authorKiyoshi Ueda <k-ueda@ct.jp.nec.com>2008-09-18 10:45:09 -0400
committerJens Axboe <jens.axboe@oracle.com>2008-10-09 08:56:18 +0200
commit32fab448e5e86694beade415e750363538ea5f49 (patch)
tree6eab6189afba893c302fa6acca1a89406fd620c6 /include/linux
parente3335de94067dbebe22e3962632ead34e832cb60 (diff)
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>
Diffstat (limited to 'include/linux')
-rw-r--r--include/linux/blkdev.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e23b838825b..e82a84c9f37 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.