block: simplify holder symlink handling

Code to manage symlinks in /sys/block/*/{holders|slaves} are overly
complex with multiple holder considerations, redundant extra
references to all involved kobjects, unused generic kobject holder
support and unnecessary mixup with bd_claim/release functionalities.

Strip it down to what's necessary (single gendisk holder) and make it
use a separate interface.  This is a step for cleaning up
bd_claim/release.  This patch makes dm-table slightly more complex but
it will be simplified again with further changes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Neil Brown <neilb@suse.de>
Acked-by: Mike Snitzer <snitzer@redhat.com>
Cc: dm-devel@redhat.com

drivers/md/dm-table.c

@@ -328,12 +328,22 @@ static int open_dev(struct dm_dev_internal *d, dev_t dev,
 	bdev = open_by_devnum(dev, d->dm_dev.mode);
 	if (IS_ERR(bdev))
 		return PTR_ERR(bdev);
-	r = bd_claim_by_disk(bdev, _claim_ptr, dm_disk(md));
-	if (r)
+
+	r = bd_claim(bdev, _claim_ptr);
+	if (r) {
 		blkdev_put(bdev, d->dm_dev.mode);
-	else
-		d->dm_dev.bdev = bdev;
-	return r;
+		return r;
+	}
+
+	r = bd_link_disk_holder(bdev, dm_disk(md));
+	if (r) {
+		bd_release(bdev);
+		blkdev_put(bdev, d->dm_dev.mode);
+		return r;
+	}
+
+	d->dm_dev.bdev = bdev;
+	return 0;
 }
 
 /*
@@ -344,7 +354,8 @@ static void close_dev(struct dm_dev_internal *d, struct mapped_device *md)
 	if (!d->dm_dev.bdev)
 		return;
 
-	bd_release_from_disk(d->dm_dev.bdev, dm_disk(md));
+	bd_unlink_disk_holder(d->dm_dev.bdev);
+	bd_release(d->dm_dev.bdev);
 	blkdev_put(d->dm_dev.bdev, d->dm_dev.mode);
 	d->dm_dev.bdev = NULL;
 }

drivers/md/md.c

@@ -1880,7 +1880,7 @@ static int bind_rdev_to_array(mdk_rdev_t * rdev, mddev_t * mddev)
 	rdev->sysfs_state = sysfs_get_dirent_safe(rdev->kobj.sd, "state");
 
 	list_add_rcu(&rdev->same_set, &mddev->disks);
-	bd_claim_by_disk(rdev->bdev, rdev->bdev->bd_holder, mddev->gendisk);
+	bd_link_disk_holder(rdev->bdev, mddev->gendisk);
 
 	/* May as well allow recovery to be retried once */
 	mddev->recovery_disabled = 0;
@@ -1907,7 +1907,7 @@ static void unbind_rdev_from_array(mdk_rdev_t * rdev)
 		MD_BUG();
 		return;
 	}
-	bd_release_from_disk(rdev->bdev, rdev->mddev->gendisk);
+	bd_unlink_disk_holder(rdev->bdev);
 	list_del_rcu(&rdev->same_set);
 	printk(KERN_INFO "md: unbind<%s>\n", bdevname(rdev->bdev,b));
 	rdev->mddev = NULL;