block: allow disk to have extended device number

Now that disk and partition handlings are mostly unified, it's easy to
allow disk to have extended device number.  This patch makes
add_disk() use extended device number if disk->minors is zero.  Both
sd and ide-disk are updated to use this.

* sd_format_disk_name() is implemented which can generically determine
  the drive name.  This removes disk number restriction stemming from
  limited device names.

* If sd index goes over SD_MAX_DISKS (which can be increased now BTW),
  sd simply doesn't initialize minors letting block layer choose
  extended device number.

* If CONFIG_DEBUG_EXT_DEVT is set, both sd and ide-disk always set
  minors to 0 and use extended device numbers.

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

1 files changed, 24 insertions, 1 deletions

diff --git a/block/genhd.c b/block/genhd.c
index eedab5b4685b..d9de3e482d1e 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -478,14 +478,37 @@ static int exact_lock(dev_t devt, void *data)
  *
  * This function registers the partitioning information in @disk
  * with the kernel.
+ *
+ * FIXME: error handling
  */
 void add_disk(struct gendisk *disk)
 {
         struct backing_dev_info *bdi;
+        dev_t devt;
         int retval;
 
+        /* minors == 0 indicates to use ext devt from part0 and should
+         * be accompanied with EXT_DEVT flag.  Make sure all
+         * parameters make sense.
+         */
+        WARN_ON(disk->minors && !(disk->major || disk->first_minor));
+        WARN_ON(!disk->minors && !(disk->flags & GENHD_FL_EXT_DEVT));
+
         disk->flags |= GENHD_FL_UP;
-        disk_to_dev(disk)->devt = MKDEV(disk->major, disk->first_minor);
+
+        retval = blk_alloc_devt(&disk->part0, &devt);
+        if (retval) {
+                WARN_ON(1);
+                return;
+        }
+        disk_to_dev(disk)->devt = devt;
+
+        /* ->major and ->first_minor aren't supposed to be
+         * dereferenced from here on, but set them just in case.
+         */
+        disk->major = MAJOR(devt);
+        disk->first_minor = MINOR(devt);
+
         blk_register_region(disk_devt(disk), disk->minors, NULL,
                             exact_match, exact_lock, disk);
         register_disk(disk);