block: add request submission interface

This patch adds blk_insert_cloned_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_insert_cloned_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>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

2 files changed, 84 insertions, 0 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 527d43e982b..b8ffbfe85ca 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1530,6 +1530,87 @@ 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_phys_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_insert_cloned_request - Helper for stacking drivers to submit a request
+ * @q:  the queue to submit the request
+ * @rq: the request being queued
+ */
+int blk_insert_cloned_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->part0.make_it_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_insert_cloned_request);
+
+/**
  * __end_that_request_first - end I/O on a request
  * @req:      the request being processed
  * @error:    %0 for success, < %0 for error
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index e82a84c9f37..964c246bc27 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -693,6 +693,9 @@ extern void __blk_put_request(struct request_queue *, struct request *);
 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_insert_cloned_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 *);