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Message-Id: <20080912.104045.41628978.k-ueda@ct.jp.nec.com>
Date: Fri, 12 Sep 2008 10:40:45 -0400 (EDT)
From: Kiyoshi Ueda <k-ueda@...jp.nec.com>
To: jens.axboe@...cle.com, agk@...hat.com,
James.Bottomley@...senPartnership.com
Cc: linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
dm-devel@...hat.com, j-nomura@...jp.nec.com, k-ueda@...jp.nec.com
Subject: [PATCH 01/13] 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). See PATCH 10.
- 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@...jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@...jp.nec.com>
Cc: Jens Axboe <jens.axboe@...cle.com>
---
block/blk-core.c | 59 +++++++++++++++++++++++++++++++++++++++++--------
include/linux/blkdev.h | 2 +
2 files changed, 52 insertions(+), 9 deletions(-)
Index: 2.6.27-rc6/block/blk-core.c
===================================================================
--- 2.6.27-rc6.orig/block/blk-core.c
+++ 2.6.27-rc6/block/blk-core.c
@@ -1862,6 +1862,22 @@ void end_request(struct request *req, in
}
EXPORT_SYMBOL(end_request);
+static int end_that_request_data(struct request *rq, int error,
+ unsigned int nr_bytes, unsigned int bidi_bytes)
+{
+ if (blk_fs_request(rq) || blk_pc_request(rq)) {
+ 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
@@ -1888,15 +1904,8 @@ static int blk_end_io(struct request *rq
struct request_queue *q = rq->q;
unsigned long flags = 0UL;
- if (blk_fs_request(rq) || blk_pc_request(rq)) {
- 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))
@@ -1981,6 +1990,38 @@ int blk_end_bidi_request(struct request
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)) {
+ /*
+ * All bios in the request have been completed.
+ * Then, members of the request are not updated.
+ * Update those members to avoid double charge of diskstat
+ * when the stacking driver calls blk_end_request()
+ * to complete the request actually.
+ */
+ rq->nr_sectors = rq->hard_nr_sectors = 0;
+ rq->current_nr_sectors = rq->hard_cur_sectors = 0;
+ rq->nr_phys_segments = rq->nr_hw_segments = 0;
+ }
+}
+EXPORT_SYMBOL_GPL(blk_update_request);
+
+/**
* blk_end_request_callback - Special helper function for tricky drivers
* @rq: the request being processed
* @error: 0 for success, < 0 for error
Index: 2.6.27-rc6/include/linux/blkdev.h
===================================================================
--- 2.6.27-rc6.orig/include/linux/blkdev.h
+++ 2.6.27-rc6/include/linux/blkdev.h
@@ -756,6 +756,8 @@ extern int blk_end_request_callback(stru
unsigned int nr_bytes,
int (drv_callback)(struct request *));
extern void blk_complete_request(struct request *);
+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.
--
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