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    SubjectRe: [PATCH 02/13] block: add request submission interface
    Kiyoshi Ueda wrote:
    > This patch adds blk_submit_request(), a generic request submission
    > interface for request stacking drivers.
    > Request-based dm will use it to submit their clones to underlying
    > devices.
    >
    > blk_rq_check_limits() is also added because it is possible that
    > the lower queue has stronger limitations than the upper queue
    > if multiple drivers are stacking at request-level.
    > Not only for blk_submit_request()'s internal use, the function
    > will be used by request-based dm when the queue limitation is
    > modified (e.g. by replacing dm's table).
    >
    >
    > Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
    > Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
    > Cc: Jens Axboe <jens.axboe@oracle.com>
    > ---
    > block/blk-core.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++
    > include/linux/blkdev.h | 2 +
    > 2 files changed, 83 insertions(+)
    >
    > 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
    > @@ -1517,6 +1517,87 @@ void submit_bio(int rw, struct bio *bio)
    > EXPORT_SYMBOL(submit_bio);
    >
    > /**
    > + * blk_rq_check_limits - Helper function to check a request for the queue limit
    > + * @q: the queue
    > + * @rq: the request being checked
    > + *
    > + * Description:
    > + * @rq may have been made based on weaker limitations of upper-level queues
    > + * in request stacking drivers, and it may violate the limitation of @q.
    > + * Since the block layer and the underlying device driver trust @rq
    > + * after it is inserted to @q, it should be checked against @q before
    > + * the insertion using this generic function.
    > + *
    > + * This function should also be useful for request stacking drivers
    > + * in some cases below, so export this fuction.
    > + * Request stacking drivers like request-based dm may change the queue
    > + * limits while requests are in the queue (e.g. dm's table swapping).
    > + * Such request stacking drivers should check those requests agaist
    > + * the new queue limits again when they dispatch those requests,
    > + * although such checkings are also done against the old queue limits
    > + * when submitting requests.
    > + */
    > +int blk_rq_check_limits(struct request_queue *q, struct request *rq)
    > +{
    > + if (rq->nr_sectors > q->max_sectors ||
    > + rq->data_len > q->max_hw_sectors << 9) {
    > + printk(KERN_ERR "%s: over max size limit.\n", __func__);
    > + return -EIO;
    > + }
    > +
    > + /*
    > + * queue's settings related to segment counting like q->bounce_pfn
    > + * may differ from that of other stacking queues.
    > + * Recalculate it to check the request correctly on this queue's
    > + * limitation.
    > + */
    > + blk_recalc_rq_segments(rq);
    > + if (rq->nr_phys_segments > q->max_phys_segments ||
    > + rq->nr_hw_segments > q->max_hw_segments) {
    > + printk(KERN_ERR "%s: over max segments limit.\n", __func__);
    > + return -EIO;
    > + }
    > +
    > + return 0;
    > +}
    > +EXPORT_SYMBOL_GPL(blk_rq_check_limits);
    > +
    > +/**
    > + * blk_submit_request - Helper for stacking drivers to submit a request
    > + * @q: the queue to submit the request
    > + * @rq: the request being queued
    > + */
    > +int blk_submit_request(struct request_queue *q, struct request *rq)
    > +{
    > + unsigned long flags;
    > +
    > + if (blk_rq_check_limits(q, rq))
    > + return -EIO;
    > +
    > +#ifdef CONFIG_FAIL_MAKE_REQUEST
    > + if (rq->rq_disk && rq->rq_disk->flags & GENHD_FL_FAIL &&
    > + should_fail(&fail_make_request, blk_rq_bytes(rq)))
    > + return -EIO;
    > +#endif
    > +
    > + spin_lock_irqsave(q->queue_lock, flags);
    > +
    > + /*
    > + * Submitting request must be dequeued before calling this function
    > + * because it will be linked to another request_queue
    > + */
    > + BUG_ON(blk_queued_rq(rq));
    > +
    > + drive_stat_acct(rq, 1);
    > + __elv_add_request(q, rq, ELEVATOR_INSERT_BACK, 0);
    > +
    > + spin_unlock_irqrestore(q->queue_lock, flags);
    > +
    > + return 0;
    > +}
    > +EXPORT_SYMBOL_GPL(blk_submit_request);
    > +

    This looks awfully similar to blk_execute_rq_nowait With an Added
    blk_rq_check_limits, minus the __generic_unplug_device() and
    q->request_fn(q) calls. Perhaps the common code could be re factored
    out? Also isn't block-exec.c a better file for this function?

    > +/**
    > * __end_that_request_first - end I/O on a request
    > * @req: 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
    > @@ -664,6 +664,8 @@ extern void __blk_put_request(struct req
    > extern struct request *blk_get_request(struct request_queue *, int, gfp_t);
    > extern void blk_insert_request(struct request_queue *, struct request *, int, void *);
    > extern void blk_requeue_request(struct request_queue *, struct request *);
    > +extern int blk_rq_check_limits(struct request_queue *q, struct request *rq);
    > +extern int blk_submit_request(struct request_queue *q, struct request *rq);
    > extern void blk_plug_device(struct request_queue *);
    > extern void blk_plug_device_unlocked(struct request_queue *);
    > extern int blk_remove_plug(struct request_queue *);
    > --
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