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Subject[PATCH 02/13] block: add request submission interface
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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);
+
+/**
* __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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