block: move __dev from disk to part0

Move disk->__dev to part0->__dev.  This simplifies bdget_disk() and
lookup_devt() and allows common sysfs attributes to be unified.
part_to_disk() is updated to handle part0 -> disk.

Updated to include a fix from Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>,
he writes:

"part0 is a "special" partition and doesn't need to have capacity set - this
fixes regression caused by "block: move __dev from disk to part0" commit."
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>

block/genhd.c

@@ -537,22 +537,15 @@ struct gendisk *get_gendisk(dev_t devt, int *partno)
  */
 extern struct block_device *bdget_disk(struct gendisk *disk, int partno)
 {
-	dev_t devt = MKDEV(0, 0);
-
-	if (partno == 0)
-		devt = disk_devt(disk);
-	else {
 	struct hd_struct *part;
+	struct block_device *bdev = NULL;
 
 	part = disk_get_part(disk, partno);
-		if (part && part->nr_sects)
-			devt = part_devt(part);
+	if (part && (part->nr_sects || partno == 0))
+		bdev = bdget(part_devt(part));
 	disk_put_part(part);
-	}
 
-	if (likely(devt != MKDEV(0, 0)))
-		return bdget(devt);
-	return NULL;
+	return bdev;
 }
 EXPORT_SYMBOL(bdget_disk);
 
@@ -1000,28 +993,19 @@ dev_t blk_lookup_devt(const char *name, int partno)
 	class_dev_iter_init(&iter, &block_class, NULL, &disk_type);
 	while ((dev = class_dev_iter_next(&iter))) {
 		struct gendisk *disk = dev_to_disk(dev);
+		struct hd_struct *part;
 
 		if (strcmp(dev->bus_id, name))
 			continue;
-		if (partno < 0 || partno >= disk_max_parts(disk))
-			continue;
-
-		if (partno == 0)
-			devt = disk_devt(disk);
-		else {
-			struct hd_struct *part;
 
 		part = disk_get_part(disk, partno);
-			if (!part || !part->nr_sects) {
-				disk_put_part(part);
-				continue;
-			}
-
+		if (part && (part->nr_sects || partno == 0)) {
 			devt = part_devt(part);
 			disk_put_part(part);
-		}
 			break;
 		}
+		disk_put_part(part);
+	}
 	class_dev_iter_exit(&iter);
 	return devt;
 }

include/linux/genhd.h

@@ -16,9 +16,9 @@
 #ifdef CONFIG_BLOCK
 
 #define kobj_to_dev(k)		container_of((k), struct device, kobj)
-#define dev_to_disk(device)	container_of((device), struct gendisk, __dev)
+#define dev_to_disk(device)	container_of((device), struct gendisk, part0.__dev)
 #define dev_to_part(device)	container_of((device), struct hd_struct, __dev)
-#define disk_to_dev(disk)	(&((disk)->__dev))
+#define disk_to_dev(disk)	(&(disk)->part0.__dev)
 #define part_to_dev(part)	(&((part)->__dev))
 
 extern struct device_type part_type;
@@ -141,7 +141,6 @@ struct gendisk {
 
 	int flags;
 	struct device *driverfs_dev;  // FIXME: remove
-	struct device __dev;
 	struct kobject *holder_dir;
 	struct kobject *slave_dir;
 
@@ -164,8 +163,12 @@ struct gendisk {
 
 static inline struct gendisk *part_to_disk(struct hd_struct *part)
 {
-	if (likely(part))
+	if (likely(part)) {
+		if (part->partno)
 			return dev_to_disk(part_to_dev(part)->parent);
+		else
+			return dev_to_disk(part_to_dev(part));
+	}
 	return NULL;
 }