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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 /block
parente3335de94067dbebe22e3962632ead34e832cb60 (diff)
downloadlinux-2.6.38-lt-ux500-32fab448e5e86694beade415e750363538ea5f49.tar.gz
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 'block')
-rw-r--r--block/blk-core.c57
1 files changed, 48 insertions, 9 deletions
diff --git a/block/blk-core.c b/block/blk-core.c
index 37fba001bdc..527d43e982b 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))
@@ -1923,6 +1932,36 @@ 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
* @error: %0 for success, < %0 for error