block: export __make_request

Avoid the hacks need for request based device mappers currently by simply
exporting the symbol instead of trying to get it through the back door.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 0e67c45..e9c3d9b 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -675,6 +675,8 @@
 extern int sg_scsi_ioctl(struct request_queue *, struct gendisk *, fmode_t,
 			 struct scsi_ioctl_command __user *);
 
+extern int __make_request(struct request_queue *q, struct bio *bio);
+
 /*
  * A queue has just exitted congestion.  Note this in the global counter of
  * congested queues, and wake up anyone who was waiting for requests to be