[PATCH -next] block: add another struct gendisk to <linux/blkdev.h>

[Randy Dunlap]

From: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>

Add a forward declaration for struct gendisk when CONFIG_BLOCK is
not set/enabled to prevent multiple (30 - 50) build warnings.

In file included from ../kernel/sched/sched.h:39:0,
                 from ../kernel/sched/core.c:9:
../include/linux/blkdev.h:1895:41: warning: 'struct gendisk' declared inside parameter list will not be visible outside of this definition or declaration
 unsigned long disk_start_io_acct(struct gendisk *disk, unsigned int sectors,
                                         ^~~~~~~

Signed-off-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: linux-block@xxxxxxxxxxxxxxx
---
 include/linux/blkdev.h |    1 +
 1 file changed, 1 insertion(+)

--- linux-next-20200528.orig/include/linux/blkdev.h
+++ linux-next-20200528/include/linux/blkdev.h
@@ -1836,6 +1836,7 @@ static inline bool blk_req_can_dispatch_
 #else /* CONFIG_BLOCK */
 
 struct block_device;
+struct gendisk;
 
 /*
  * stubs for when the block layer is configured out