block: add a disk_has_partscan helper

Add a helper to check if partition scanning is enabled instead of
open coding the check in a few places.  This now always checks for
the hidden flag even if all but one of the callers are never reachable
for hidden gendisks.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20240502130033.1958492-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/blkdev.h

@@ -230,6 +230,19 @@ static inline unsigned int disk_openers(struct gendisk *disk)
 	return atomic_read(&disk->part0->bd_openers);
 }
 
+/**
+ * disk_has_partscan - return %true if partition scanning is enabled on a disk
+ * @disk: disk to check
+ *
+ * Returns %true if partitions scanning is enabled for @disk, or %false if
+ * partition scanning is disabled either permanently or temporarily.
+ */
+static inline bool disk_has_partscan(struct gendisk *disk)
+{
+	return !(disk->flags & (GENHD_FL_NO_PART | GENHD_FL_HIDDEN)) &&
+		!test_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
+}
+
 /*
  * The gendisk is refcounted by the part0 block_device, and the bd_device
  * therein is also used for device model presentation in sysfs.