block: genhd: Add disk/partition specific uevent callbacks for partition info

For disk devices, a new uevent parameter 'NPARTS' specifies the number
of partitions detected by the kernel. Partition devices get 'PARTN' which
specifies the partitions index in the table, and 'PARTNAME', which
specifies PARTNAME specifices the partition name of a partition device

Signed-off-by: Dima Zavin <dima@android.com>
diff --git a/block/genhd.c b/block/genhd.c
index df9816e..dba0262 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1107,6 +1107,22 @@
 		blk_put_queue(disk->queue);
 	kfree(disk);
 }
+
+static int disk_uevent(struct device *dev, struct kobj_uevent_env *env)
+{
+	struct gendisk *disk = dev_to_disk(dev);
+	struct disk_part_iter piter;
+	struct hd_struct *part;
+	int cnt = 0;
+
+	disk_part_iter_init(&piter, disk, 0);
+	while((part = disk_part_iter_next(&piter)))
+		cnt++;
+	disk_part_iter_exit(&piter);
+	add_uevent_var(env, "NPARTS=%u", cnt);
+	return 0;
+}
+
 struct class block_class = {
 	.name		= "block",
 };
@@ -1125,6 +1141,7 @@
 	.groups		= disk_attr_groups,
 	.release	= disk_release,
 	.devnode	= block_devnode,
+	.uevent		= disk_uevent,
 };
 
 #ifdef CONFIG_PROC_FS