ll_rw_blk: add io_context private pointer

To be used by as/cfq as they see fit.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/ll_rw_blk.c

@@ -3741,6 +3741,7 @@ static struct io_context *current_io_context(gfp_t gfp_flags, int node)
 		ret->nr_batch_requests = 0; /* because this is 0 */
 		ret->aic = NULL;
 		ret->cic_root.rb_node = NULL;
+		ret->ioc_data = NULL;
 		/* make sure set_task_ioprio() sees the settings above */
 		smp_wmb();
 		tsk->io_context = ret;

include/linux/blkdev.h

@@ -116,6 +116,7 @@ struct io_context {
 
 	struct as_io_context *aic;
 	struct rb_root cic_root;
+	void *ioc_data;
 };
 
 void put_io_context(struct io_context *ioc);