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, 4 insertions, 3 deletions

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index ace998ce59f6..a78caad29996 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1146,7 +1146,7 @@ static void unlock_fs(struct mapped_device *md);
 
 static void free_dev(struct mapped_device *md)
 {
-        int minor = md->disk->first_minor;
+        int minor = MINOR(disk_devt(md->disk));
 
         if (md->suspended_bdev) {
                 unlock_fs(md);
@@ -1267,7 +1267,7 @@ static struct mapped_device *dm_find_md(dev_t dev)
 
         md = idr_find(&_minor_idr, minor);
         if (md && (md == MINOR_ALLOCED ||
-                   (dm_disk(md)->first_minor != minor) ||
+                   (MINOR(disk_devt(dm_disk(md))) != minor) ||
                    test_bit(DMF_FREEING, &md->flags))) {
                 md = NULL;
                 goto out;
@@ -1318,7 +1318,8 @@ void dm_put(struct mapped_device *md)
 
         if (atomic_dec_and_lock(&md->holders, &_minor_lock)) {
                 map = dm_get_table(md);
-                idr_replace(&_minor_idr, MINOR_ALLOCED, dm_disk(md)->first_minor);
+                idr_replace(&_minor_idr, MINOR_ALLOCED,
+                            MINOR(disk_devt(dm_disk(md))));
                 set_bit(DMF_FREEING, &md->flags);
                 spin_unlock(&_minor_lock);
                 if (!dm_suspended(md)) {