[PATCH RFC 1/3] block: reuse one scheduler/flush field for private request's data

[Ming Lei <ming.lei@redhat.com>]

Reuse one union shared by elevator and flush request for data of
private request. Private request won't enter IO scheduler and never
be a flush request, so reuse the space for data of private request.

This field is added to pass driver private info for private request
only.

Cc: James Smart <james.smart@broadcom.com>
Cc: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/blkdev.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 6a4f7abbdcf7..ce708dc10bdc 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -177,7 +177,8 @@ struct request {
 	 * Three pointers are available for the IO schedulers, if they need
 	 * more they have to dynamically allocate it.  Flush requests are
 	 * never put on the IO scheduler. So let the flush fields share
-	 * space with the elevator data.
+	 * space with the elevator data. Private request are never put on
+	 * IO scheduler, and not be a flush request.
 	 */
 	union {
 		struct {
@@ -190,6 +191,9 @@ struct request {
 			struct list_head	list;
 			rq_end_io_fn		*saved_end_io;
 		} flush;
+
+		/* used for private request only */
+		unsigned long private_rq_data;
 	};
 
 	struct gendisk *rq_disk;
-- 
2.20.1