block: don't depend on consecutive minor space

* Implement disk_devt() and part_devt() and use them to directly
  access devt instead of computing it from ->major and ->first_minor.

  Note that all references to ->major and ->first_minor outside of
  block layer is used to determine devt of the disk (the part0) and as
  ->major and ->first_minor will continue to represent devt for the
  disk, converting these users aren't strictly necessary.  However,
  convert them for consistency.

* Implement disk_max_parts() to avoid directly deferencing
  genhd->minors.

* Update bdget_disk() such that it doesn't assume consecutive minor
  space.

* Move devt computation from register_disk() to add_disk() and make it
  the only one (all other usages use the initially determined value).

These changes clean up the code and will help disk->part dereference
fix and extended block device numbers.

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

1 files changed, 21 insertions, 6 deletions

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index d1723c0a8600..0ff75329199c 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -111,10 +111,14 @@ struct hd_struct {
 #define GENHD_FL_FAIL                           64
 
 struct gendisk {
+        /* major, first_minor and minors are input parameters only,
+         * don't use directly.  Use disk_devt() and disk_max_parts().
+         */
         int major;                      /* major number of driver */
         int first_minor;
         int minors;                     /* maximum number of minors, =1 for
                                          * disks that can't be partitioned. */
+
         char disk_name[32];             /* name of major driver */
         struct hd_struct **part;        /* [indexed by minor - 1] */
         struct block_device_operations *fops;
@@ -152,6 +156,21 @@ static inline struct gendisk *part_to_disk(struct hd_struct *part)
         return NULL;
 }
 
+static inline int disk_max_parts(struct gendisk *disk)
+{
+        return disk->minors - 1;
+}
+
+static inline dev_t disk_devt(struct gendisk *disk)
+{
+        return disk->dev.devt;
+}
+
+static inline dev_t part_devt(struct hd_struct *part)
+{
+        return part->dev.devt;
+}
+
 /* 
  * Macros to operate on percpu disk statistics:
  *
@@ -163,7 +182,7 @@ static inline struct hd_struct *disk_map_sector(struct gendisk *gendiskp,
 {
         struct hd_struct *part;
         int i;
-        for (i = 0; i < gendiskp->minors - 1; i++) {
+        for (i = 0; i < disk_max_parts(gendiskp); i++) {
                 part = gendiskp->part[i];
                 if (part && part->start_sect <= sector
                     && sector < part->start_sect + part->nr_sects)
@@ -366,6 +385,7 @@ extern void add_disk(struct gendisk *disk);
 extern void del_gendisk(struct gendisk *gp);
 extern void unlink_gendisk(struct gendisk *gp);
 extern struct gendisk *get_gendisk(dev_t dev, int *partno);
+extern struct block_device *bdget_disk(struct gendisk *disk, int partno);
 
 extern void set_device_ro(struct block_device *bdev, int flag);
 extern void set_disk_ro(struct gendisk *disk, int flag);
@@ -553,11 +573,6 @@ extern void blk_register_region(dev_t devt, unsigned long range,
                         void *data);
 extern void blk_unregister_region(dev_t devt, unsigned long range);
 
-static inline struct block_device *bdget_disk(struct gendisk *disk, int partno)
-{
-        return bdget(MKDEV(disk->major, disk->first_minor) + partno);
-}
-
 #else /* CONFIG_BLOCK */
 
 static inline void printk_all_partitions(void) { }