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block: clean up request completion API
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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.

   blk_end_bidi_request() is identical to blk_end_io().  Collapse
   blk_end_io() into blk_end_bidi_request(), separate out request
   update into internal helper blk_update_bidi_request() and add
   __blk_end_bidi_request().  Redefine [__]blk_end_request() as thin
   inline wrappers around [__]blk_end_bidi_request().

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 - blk_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().

API further cleaned up per Christoph's suggestion.

[ 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>
Cc: Christoph Hellwig <hch@infradead.org>
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Tejun Heo authored and Jens Axboe committed Apr 28, 2009
1 parent 0b302d5 commit 2e60e02
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226 changes: 75 additions & 151 deletions block/blk-core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1808,25 +1808,35 @@ 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);

/*
Expand Down Expand Up @@ -1903,8 +1913,16 @@ 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
Expand All @@ -1918,29 +1936,31 @@ 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;
return true;
}
EXPORT_SYMBOL_GPL(blk_update_request);

static int end_that_request_data(struct request *rq, int error,
unsigned int nr_bytes, unsigned int bidi_bytes)
static bool blk_update_bidi_request(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;
if (blk_update_request(rq, error, nr_bytes))
return true;

/* 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;
}
/* 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;

return 0;
add_disk_randomness(rq->rq_disk);

return false;
}

/*
* queue lock must be held
*/
static void end_that_request_last(struct request *req, int error)
static void blk_finish_request(struct request *req, int error)
{
if (blk_rq_tagged(req))
blk_queue_end_tag(req->q, req);
Expand All @@ -1966,161 +1986,65 @@ static void end_that_request_last(struct request *req, int error)
}

/**
* 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
* blk_end_bidi_request - Complete a bidi request
* @rq: the request to complete
* @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.
* If @rq has leftover, sets it up for the next range of segments.
* 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:
* %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 - still buffers pending for this request
**/
static int blk_end_io(struct request *rq, int error, unsigned int nr_bytes,
unsigned int bidi_bytes)
bool blk_end_bidi_request(struct request *rq, int error,
unsigned int nr_bytes, unsigned int bidi_bytes)
{
struct request_queue *q = rq->q;
unsigned long flags = 0UL;

if (end_that_request_data(rq, error, nr_bytes, bidi_bytes))
return 1;
unsigned long flags;

add_disk_randomness(rq->rq_disk);
if (blk_update_bidi_request(rq, error, nr_bytes, bidi_bytes))
return true;

spin_lock_irqsave(q->queue_lock, flags);
end_that_request_last(rq, error);
blk_finish_request(rq, error);
spin_unlock_irqrestore(q->queue_lock, flags);

return 0;
}

/**
* 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;

add_disk_randomness(rq->rq_disk);

end_that_request_last(rq, error);

return 0;
return false;
}
EXPORT_SYMBOL_GPL(__blk_end_request);
EXPORT_SYMBOL_GPL(blk_end_bidi_request);

/**
* blk_end_bidi_request - Helper function for drivers to complete bidi request.
* @rq: the bidi request being processed
* __blk_end_bidi_request - Complete a bidi request with queue lock held
* @rq: the request to complete
* @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.
* Identical to blk_end_bidi_request() except that queue lock is
* assumed to be locked on entry and remains so on return.
*
* 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.
* %false - we are done with this request
* %true - still buffers pending for this request
**/
void end_request(struct request *req, int uptodate)
bool __blk_end_bidi_request(struct request *rq, int error,
unsigned int nr_bytes, unsigned int bidi_bytes)
{
int error = 0;
if (blk_update_bidi_request(rq, error, nr_bytes, bidi_bytes))
return true;

if (uptodate <= 0)
error = uptodate ? uptodate : -EIO;
blk_finish_request(rq, error);

__blk_end_request(req, error, req->hard_cur_sectors << 9);
}
EXPORT_SYMBOL(end_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;
}
return false;
}
EXPORT_SYMBOL_GPL(blk_update_request);
EXPORT_SYMBOL_GPL(__blk_end_bidi_request);

void blk_rq_bio_prep(struct request_queue *q, struct request *rq,
struct bio *bio)
Expand Down
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