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, 23 insertions, 17 deletions

diff --git a/block/genhd.c b/block/genhd.c
index 0a2f16bd54b7..65b7386c26d8 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -54,10 +54,10 @@ struct hd_struct *disk_get_part(struct gendisk *disk, int partno)
 {
 	struct hd_struct *part;
 
-	if (unlikely(partno < 1 || partno > disk_max_parts(disk)))
+	if (unlikely(partno < 0 || partno >= disk_max_parts(disk)))
 		return NULL;
 	rcu_read_lock();
-	part = rcu_dereference(disk->__part[partno - 1]);
+	part = rcu_dereference(disk->__part[partno]);
 	if (part)
 		get_device(part_to_dev(part));
 	rcu_read_unlock();
@@ -85,8 +85,10 @@ void disk_part_iter_init(struct disk_part_iter *piter, struct gendisk *disk,
 
 	if (flags & DISK_PITER_REVERSE)
 		piter->idx = disk_max_parts(piter->disk) - 1;
-	else
+	else if (flags & DISK_PITER_INCL_PART0)
 		piter->idx = 0;
+	else
+		piter->idx = 1;
 
 	piter->flags = flags;
 }
@@ -114,7 +116,10 @@ struct hd_struct *disk_part_iter_next(struct disk_part_iter *piter)
 	/* determine iteration parameters */
 	if (piter->flags & DISK_PITER_REVERSE) {
 		inc = -1;
-		end = -1;
+		if (piter->flags & DISK_PITER_INCL_PART0)
+			end = -1;
+		else
+			end = 0;
 	} else {
 		inc = 1;
 		end = disk_max_parts(piter->disk);
@@ -177,7 +182,7 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
 {
 	int i;
 
-	for (i = 0; i < disk_max_parts(disk); i++) {
+	for (i = 1; i < disk_max_parts(disk); i++) {
 		struct hd_struct *part = rcu_dereference(disk->__part[i]);
 
 		if (part && part->start_sect <= sector &&
@@ -669,7 +674,7 @@ static int show_partition(struct seq_file *seqf, void *v)
 	char buf[BDEVNAME_SIZE];
 
 	/* Don't show non-partitionable removeable devices or empty devices */
-	if (!get_capacity(sgp) || (!disk_max_parts(sgp) &&
+	if (!get_capacity(sgp) || (!disk_partitionable(sgp) &&
 				   (sgp->flags & GENHD_FL_REMOVABLE)))
 		return 0;
 	if (sgp->flags & GENHD_FL_SUPPRESS_PARTITION_INFO)
@@ -742,7 +747,7 @@ static ssize_t disk_ext_range_show(struct device *dev,
 {
 	struct gendisk *disk = dev_to_disk(dev);
 
-	return sprintf(buf, "%d\n", disk_max_parts(disk) + 1);
+	return sprintf(buf, "%d\n", disk_max_parts(disk));
 }
 
 static ssize_t disk_removable_show(struct device *dev,
@@ -998,7 +1003,7 @@ dev_t blk_lookup_devt(const char *name, int partno)
 
 		if (strcmp(dev->bus_id, name))
 			continue;
-		if (partno < 0 || partno > disk_max_parts(disk))
+		if (partno < 0 || partno >= disk_max_parts(disk))
 			continue;
 
 		if (partno == 0)
@@ -1045,21 +1050,22 @@ struct gendisk *alloc_disk_ext_node(int minors, int ext_minors, int node_id)
 				GFP_KERNEL | __GFP_ZERO, node_id);
 	if (disk) {
 		int tot_minors = minors + ext_minors;
+		int size = tot_minors * sizeof(struct hd_struct *);
 
 		if (!init_disk_stats(disk)) {
 			kfree(disk);
 			return NULL;
 		}
-		if (tot_minors > 1) {
-			int size = (tot_minors - 1) * sizeof(struct hd_struct *);
-			disk->__part = kmalloc_node(size,
-				GFP_KERNEL | __GFP_ZERO, node_id);
-			if (!disk->__part) {
-				free_disk_stats(disk);
-				kfree(disk);
-				return NULL;
-			}
+
+		disk->__part = kmalloc_node(size, GFP_KERNEL | __GFP_ZERO,
+					    node_id);
+		if (!disk->__part) {
+			free_disk_stats(disk);
+			kfree(disk);
+			return NULL;
 		}
+		disk->__part[0] = &disk->part0;
+
 		disk->minors = minors;
 		disk->ext_minors = ext_minors;
 		rand_initialize_disk(disk);