block: introduce partition 0

genhd and partition code handled disk and partitions separately.  All
information about the whole disk was in struct genhd and partitions in
struct hd_struct.  However, the whole disk (part0) and other
partitions have a lot in common and the data structures end up having
good number of common fields and thus separate code paths doing the
same thing.  Also, the partition array was indexed by partno - 1 which
gets pretty confusing at times.

This patch introduces partition 0 and makes the partition array
indexed by partno.  Following patches will unify the handling of disk
and parts piece-by-piece.

This patch also implements disk_partitionable() which tests whether a
disk is partitionable.  With coming dynamic partition array change,
the most common usage of disk_max_parts() will be testing whether a
disk is partitionable and the number of max partitions will become
much less important.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 9 insertions, 2 deletions

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index e4e18c509ac..9e866a2aee5 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -127,12 +127,13 @@ struct gendisk {
 
 	char disk_name[32];		/* name of major driver */
 
-	/* Array of pointers to partitions indexed by partno - 1.
+	/* Array of pointers to partitions indexed by partno.
 	 * Protected with matching bdev lock but stat and other
 	 * non-critical accesses use RCU.  Always access through
 	 * helpers.
 	 */
 	struct hd_struct **__part;
+	struct hd_struct part0;
 
 	struct block_device_operations *fops;
 	struct request_queue *queue;
@@ -171,7 +172,12 @@ static inline struct gendisk *part_to_disk(struct hd_struct *part)
 
 static inline int disk_max_parts(struct gendisk *disk)
 {
-	return disk->minors + disk->ext_minors - 1;
+	return disk->minors + disk->ext_minors;
+}
+
+static inline bool disk_partitionable(struct gendisk *disk)
+{
+	return disk_max_parts(disk) > 1;
 }
 
 static inline dev_t disk_devt(struct gendisk *disk)
@@ -197,6 +203,7 @@ static inline void disk_put_part(struct hd_struct *part)
  */
 #define DISK_PITER_REVERSE	(1 << 0) /* iterate in the reverse direction */
 #define DISK_PITER_INCL_EMPTY	(1 << 1) /* include 0-sized parts */
+#define DISK_PITER_INCL_PART0	(1 << 2) /* include partition 0 */
 
 struct disk_part_iter {
 	struct gendisk		*disk;