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Subject[PATCH 09/14] block: clean up request completion API
Date
Request completion has gone through several changes and became a bit
messy over the time. Clean it up.

1. end_that_request_data() is a thin wrapper around
end_that_request_data_first() which checks whether bio is NULL
before doing anything and handles bidi completion.
blk_update_request() is a thin wrapper around
end_that_request_data() which clears nr_sectors on the last
iteration but doesn't use the bidi completion.

Clean it up by moving the initial bio NULL check and nr_sectors
clearing on the last iteration into end_that_request_data() and
renaming it to blk_update_request(), which makes blk_end_io() the
only user of end_that_request_data(). Collapse
end_that_request_data() into blk_end_io().

2. There are four visible completion variants - blk_end_request(),
__blk_end_request(), blk_end_bidi_request() and end_request().
blk_end_request() and blk_end_bidi_request() uses blk_end_request()
as the backend but __blk_end_request() and end_request() use
separate implementation in __blk_end_request() due to different
locking rules.

Make blk_end_io() handle both cases thus all four public completion
functions are thin wrappers around blk_end_io(). Rename
blk_end_io() to __blk_end_io() and export it and inline all public
completion functions.

3. As the whole request issue/completion usages are about to be
modified and audited, it's a good chance to convert completion
functions return bool which better indicates the intended meaning
of return values.

4. The function name end_that_request_last() is from the days when it
was a public interface and slighly confusing. Give it a proper
internal name - finish_request().

5. Add description explaning that blk_end_bidi_request() can be safely
used for uni requests as suggested by Boaz Harrosh.

The only visible behavior change is from #1. nr_sectors counts are
cleared after the final iteration no matter which function is used to
complete the request. I couldn't find any place where the code
assumes those nr_sectors counters contain the values for the last
segment and this change is good as it makes the API much more
consistent as the end result is now same whether a request is
completed using [__]blk_end_request() alone or in combination with
blk_update_request().

[ Impact: cleanup, rq->*nr_sectors always updated after req completion ]

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Boaz Harrosh <bharrosh@panasas.com>
---
block/blk-core.c | 215 ++++++++++++------------------------------------
include/linux/blkdev.h | 117 +++++++++++++++++++++++---
2 files changed, 157 insertions(+), 175 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c
index 0f402c2..274888b 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1806,25 +1806,35 @@ void elv_dequeue_request(struct request_queue *q, struct request *rq)
}

/**
- * __end_that_request_first - end I/O on a request
- * @req: the request being processed
+ * 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
+ * @nr_bytes: number of bytes to complete @rq
*
* Description:
- * Ends I/O on a number of bytes attached to @req, and sets it up
- * for the next range of segments (if any) in the cluster.
+ * 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.
+ *
+ * Passing the result of blk_rq_bytes() as @nr_bytes guarantees
+ * %false return from this function.
*
* Return:
- * %0 - we are done with this request, call end_that_request_last()
- * %1 - still buffers pending for this request
+ * %false - this request doesn't have any more data
+ * %true - this request has more data
**/
-static int __end_that_request_first(struct request *req, int error,
- int nr_bytes)
+bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
{
int total_bytes, bio_nbytes, next_idx = 0;
struct bio *bio;

+ if (!req->bio)
+ return false;
+
trace_block_rq_complete(req->q, req);

/*
@@ -1901,8 +1911,16 @@ static int __end_that_request_first(struct request *req, int error,
/*
* completely done
*/
- if (!req->bio)
- return 0;
+ if (!req->bio) {
+ /*
+ * Reset counters so that the request stacking driver
+ * can find how many bytes remain in the request
+ * later.
+ */
+ req->nr_sectors = req->hard_nr_sectors = 0;
+ req->current_nr_sectors = req->hard_cur_sectors = 0;
+ return false;
+ }

/*
* if the request wasn't completed, update state
@@ -1916,29 +1934,14 @@ static int __end_that_request_first(struct request *req, int error,

blk_recalc_rq_sectors(req, total_bytes >> 9);
blk_recalc_rq_segments(req);
- return 1;
-}
-
-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;
+ return true;
}
+EXPORT_SYMBOL_GPL(blk_update_request);

/*
* queue lock must be held
*/
-static void end_that_request_last(struct request *req, int error)
+static void finish_request(struct request *req, int error)
{
if (blk_rq_tagged(req))
blk_queue_end_tag(req->q, req);
@@ -1964,161 +1967,47 @@ static void end_that_request_last(struct request *req, int error)
}

/**
- * blk_end_io - Generic end_io function to complete a request.
+ * __blk_end_io - Generic end_io function to complete a request.
* @rq: the request being processed
* @error: %0 for success, < %0 for error
* @nr_bytes: number of bytes to complete @rq
* @bidi_bytes: number of bytes to complete @rq->next_rq
+ * @locked: whether rq->q->queue_lock is held on entry
*
* Description:
* Ends I/O on a number of bytes attached to @rq and @rq->next_rq.
* If @rq has leftover, sets it up for the next range of segments.
*
* Return:
- * %0 - we are done with this request
- * %1 - this request is not freed yet, it still has pending buffers.
+ * %false - we are done with this request
+ * %true - this request is not freed yet, it still has pending buffers.
**/
-static int blk_end_io(struct request *rq, int error, unsigned int nr_bytes,
- unsigned int bidi_bytes)
+bool __blk_end_io(struct request *rq, int error, unsigned int nr_bytes,
+ unsigned int bidi_bytes, bool locked)
{
struct request_queue *q = rq->q;
unsigned long flags = 0UL;

- if (end_that_request_data(rq, error, nr_bytes, bidi_bytes))
- return 1;
-
- add_disk_randomness(rq->rq_disk);
-
- spin_lock_irqsave(q->queue_lock, flags);
- end_that_request_last(rq, error);
- spin_unlock_irqrestore(q->queue_lock, flags);
-
- return 0;
-}
+ if (blk_update_request(rq, error, nr_bytes))
+ return true;

-/**
- * blk_end_request - Helper function for drivers to complete the request.
- * @rq: the request being processed
- * @error: %0 for success, < %0 for error
- * @nr_bytes: number of bytes to complete
- *
- * Description:
- * Ends I/O on a number of bytes attached to @rq.
- * If @rq has leftover, sets it up for the next range of segments.
- *
- * Return:
- * %0 - we are done with this request
- * %1 - still buffers pending for this request
- **/
-int blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
-{
- return blk_end_io(rq, error, nr_bytes, 0);
-}
-EXPORT_SYMBOL_GPL(blk_end_request);
-
-/**
- * __blk_end_request - Helper function for drivers to complete the request.
- * @rq: the request being processed
- * @error: %0 for success, < %0 for error
- * @nr_bytes: number of bytes to complete
- *
- * Description:
- * Must be called with queue lock held unlike blk_end_request().
- *
- * Return:
- * %0 - we are done with this request
- * %1 - still buffers pending for this request
- **/
-int __blk_end_request(struct request *rq, int error, unsigned int nr_bytes)
-{
- if (rq->bio && __end_that_request_first(rq, error, nr_bytes))
- return 1;
+ /* Bidi request must be completed as a whole */
+ if (unlikely(blk_bidi_rq(rq)) &&
+ blk_update_request(rq->next_rq, error, bidi_bytes))
+ return true;

add_disk_randomness(rq->rq_disk);

- end_that_request_last(rq, error);
-
- return 0;
-}
-EXPORT_SYMBOL_GPL(__blk_end_request);
-
-/**
- * blk_end_bidi_request - Helper function for drivers to complete bidi request.
- * @rq: the bidi request being processed
- * @error: %0 for success, < %0 for error
- * @nr_bytes: number of bytes to complete @rq
- * @bidi_bytes: number of bytes to complete @rq->next_rq
- *
- * Description:
- * Ends I/O on a number of bytes attached to @rq and @rq->next_rq.
- *
- * Return:
- * %0 - we are done with this request
- * %1 - still buffers pending for this request
- **/
-int blk_end_bidi_request(struct request *rq, int error, unsigned int nr_bytes,
- unsigned int bidi_bytes)
-{
- return blk_end_io(rq, error, nr_bytes, bidi_bytes);
-}
-EXPORT_SYMBOL_GPL(blk_end_bidi_request);
-
-/**
- * end_request - end I/O on the current segment of the request
- * @req: the request being processed
- * @uptodate: error value or %0/%1 uptodate flag
- *
- * Description:
- * Ends I/O on the current segment of a request. If that is the only
- * remaining segment, the request is also completed and freed.
- *
- * This is a remnant of how older block drivers handled I/O completions.
- * Modern drivers typically end I/O on the full request in one go, unless
- * they have a residual value to account for. For that case this function
- * isn't really useful, unless the residual just happens to be the
- * full current segment. In other words, don't use this function in new
- * code. Use blk_end_request() or __blk_end_request() to end a request.
- **/
-void end_request(struct request *req, int uptodate)
-{
- int error = 0;
-
- if (uptodate <= 0)
- error = uptodate ? uptodate : -EIO;
-
- __blk_end_request(req, error, req->hard_cur_sectors << 9);
-}
-EXPORT_SYMBOL(end_request);
+ if (!locked) {
+ spin_lock_irqsave(q->queue_lock, flags);
+ finish_request(rq, error);
+ spin_unlock_irqrestore(q->queue_lock, flags);
+ } else
+ finish_request(rq, error);

-/**
- * 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;
- }
+ return false;
}
-EXPORT_SYMBOL_GPL(blk_update_request);
+EXPORT_SYMBOL_GPL(__blk_end_io);

void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
struct bio *bio)
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e24f56d..0d94ad6 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -837,27 +837,120 @@ extern unsigned int blk_rq_bytes(struct request *rq);
extern unsigned int blk_rq_cur_bytes(struct request *rq);

/*
- * blk_end_request() and friends.
- * __blk_end_request() and end_request() must be called with
- * the request queue spinlock acquired.
+ * Request completion related functions.
+ *
+ * blk_update_request() completes given number of bytes and updates
+ * the request without completing it.
+ *
+ * blk_end_request() and friends. __blk_end_request() and
+ * end_request() must be called with the request queue spinlock
+ * acquired.
*
* Several drivers define their own end_request and call
* blk_end_request() for parts of the original function.
* This prevents code duplication in drivers.
*/
-extern int blk_end_request(struct request *rq, int error,
- unsigned int nr_bytes);
-extern int __blk_end_request(struct request *rq, int error,
- unsigned int nr_bytes);
-extern int blk_end_bidi_request(struct request *rq, int error,
- unsigned int nr_bytes, unsigned int bidi_bytes);
-extern void end_request(struct request *, int);
+extern bool blk_update_request(struct request *rq, int error,
+ unsigned int nr_bytes);
+
+/* internal function, subject to change, don't ever use directly */
+extern bool __blk_end_io(struct request *rq, int error,
+ unsigned int nr_bytes, unsigned int bidi_bytes,
+ bool locked);
+
+/**
+ * blk_end_request - Helper function for drivers to complete the request.
+ * @rq: the request being processed
+ * @error: %0 for success, < %0 for error
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ * Ends I/O on a number of bytes attached to @rq.
+ * If @rq has leftover, sets it up for the next range of segments.
+ *
+ * Return:
+ * %false - we are done with this request
+ * %true - still buffers pending for this request
+ **/
+static inline bool blk_end_request(struct request *rq, int error,
+ unsigned int nr_bytes)
+{
+ return __blk_end_io(rq, error, nr_bytes, 0, false);
+}
+
+/**
+ * __blk_end_request - Helper function for drivers to complete the request.
+ * @rq: the request being processed
+ * @error: %0 for success, < %0 for error
+ * @nr_bytes: number of bytes to complete
+ *
+ * Description:
+ * Must be called with queue lock held unlike blk_end_request().
+ *
+ * Return:
+ * %false - we are done with this request
+ * %true - still buffers pending for this request
+ **/
+static inline bool __blk_end_request(struct request *rq, int error,
+ unsigned int nr_bytes)
+{
+ return __blk_end_io(rq, error, nr_bytes, 0, true);
+}
+
+/**
+ * blk_end_bidi_request - Helper function for drivers to complete bidi request.
+ * @rq: the bidi request being processed
+ * @error: %0 for success, < %0 for error
+ * @nr_bytes: number of bytes to complete @rq
+ * @bidi_bytes: number of bytes to complete @rq->next_rq
+ *
+ * Description:
+ * Ends I/O on a number of bytes attached to @rq and @rq->next_rq.
+ * Drivers that supports bidi can safely call this member for any
+ * type of request, bidi or uni. In the later case @bidi_bytes is
+ * just ignored.
+ *
+ * Return:
+ * %false - we are done with this request
+ * %true - still buffers pending for this request
+ **/
+static inline bool blk_end_bidi_request(struct request *rq, int error,
+ unsigned int nr_bytes,
+ unsigned int bidi_bytes)
+{
+ return __blk_end_io(rq, error, nr_bytes, bidi_bytes, false);
+}
+
+/**
+ * end_request - end I/O on the current segment of the request
+ * @rq: the request being processed
+ * @uptodate: error value or %0/%1 uptodate flag
+ *
+ * Description:
+ * Ends I/O on the current segment of a request. If that is the only
+ * remaining segment, the request is also completed and freed.
+ *
+ * This is a remnant of how older block drivers handled I/O completions.
+ * Modern drivers typically end I/O on the full request in one go, unless
+ * they have a residual value to account for. For that case this function
+ * isn't really useful, unless the residual just happens to be the
+ * full current segment. In other words, don't use this function in new
+ * code. Use blk_end_request() or __blk_end_request() to end a request.
+ **/
+static inline void end_request(struct request *rq, int uptodate)
+{
+ int error = 0;
+
+ if (uptodate <= 0)
+ error = uptodate ? uptodate : -EIO;
+
+ __blk_end_io(rq, error, rq->hard_cur_sectors << 9, 0, true);
+}
+
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);

/*
* Access functions for manipulating queue properties
--
1.6.0.2


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