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>
diff --git a/block/blk-core.c b/block/blk-core.c
index 37fba00..527d43e 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1806,6 +1806,22 @@
}
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 @@
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 @@
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