block: cleanup how md_autodetect_dev is called

Add a new include/linux/raid/detect.h header to declare the
md_autodetect_dev prototype which can be shared between md and
the partition code.  Then use IS_BUILTIN to call it instead of the
ifdef magic.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/partition-generic.c

@@ -18,14 +18,11 @@
 #include <linux/ctype.h>
 #include <linux/genhd.h>
 #include <linux/blktrace_api.h>
+#include <linux/raid/detect.h>
 #include "blk.h"
 
 #include "partitions/check.h"
 
-#ifdef CONFIG_BLK_DEV_MD
-extern void md_autodetect_dev(dev_t dev);
-#endif
- 
 static ssize_t part_partition_show(struct device *dev,
 				   struct device_attribute *attr, char *buf)
 {
@@ -407,10 +404,10 @@ static bool blk_add_partition(struct gendisk *disk, struct block_device *bdev,
 		return true;
 	}
 
-#ifdef CONFIG_BLK_DEV_MD
-	if (state->parts[p].flags & ADDPART_FLAG_RAID)
+	if (IS_BUILTIN(CONFIG_BLK_DEV_MD) &&
+	    (state->parts[p].flags & ADDPART_FLAG_RAID))
 		md_autodetect_dev(part_to_dev(part)->devt);
-#endif
+
 	return true;
 }
 

drivers/md/md.c

@@ -58,6 +58,7 @@
 #include <linux/delay.h>
 #include <linux/raid/md_p.h>
 #include <linux/raid/md_u.h>
+#include <linux/raid/detect.h>
 #include <linux/slab.h>
 #include <linux/percpu-refcount.h>
 

include/linux/raid/detect.h

+/* SPDX-License-Identifier: GPL-2.0 */
+
+void md_autodetect_dev(dev_t dev);