loop: cleanup partitions when detaching loop device

Any partitions added by user space to the loop device were being
left in place after detaching the loop device.  This was because
the detach path issued a BLKRRPART to clean up partitions if
LO_FLAGS_PARTSCAN was set, meaning that the partitions were auto
scanned on attach.  Replace this BLKRRPART with code that
unconditionally cleans up partitions on detach instead.
Signed-off-by: Phillip Susi <psusi@ubuntu.com>

Modified by Jens to export delete_partition().
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/partition-generic.c

@@ -257,6 +257,7 @@ void delete_partition(struct gendisk *disk, int partno)
 
 	hd_struct_put(part);
 }
+EXPORT_SYMBOL(delete_partition);
 
 static ssize_t whole_disk_show(struct device *dev,
 			       struct device_attribute *attr, char *buf)

drivers/block/loop.c

@@ -1044,12 +1044,29 @@ static int loop_clr_fd(struct loop_device *lo)
 	lo->lo_state = Lo_unbound;
 	/* This is safe: open() is still holding a reference. */
 	module_put(THIS_MODULE);
-	if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev)
-		ioctl_by_bdev(bdev, BLKRRPART, 0);
 	lo->lo_flags = 0;
 	if (!part_shift)
 		lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
 	mutex_unlock(&lo->lo_ctl_mutex);
+
+	/*
+	 * Remove all partitions, since BLKRRPART won't remove user
+	 * added partitions when max_part=0
+	 */
+	if (bdev) {
+		struct disk_part_iter piter;
+		struct hd_struct *part;
+
+		mutex_lock_nested(&bdev->bd_mutex, 1);
+		invalidate_partition(bdev->bd_disk, 0);
+		disk_part_iter_init(&piter, bdev->bd_disk,
+					DISK_PITER_INCL_EMPTY);
+		while ((part = disk_part_iter_next(&piter)))
+			delete_partition(bdev->bd_disk, part->partno);
+		disk_part_iter_exit(&piter);
+		mutex_unlock(&bdev->bd_mutex);
+	}
+
 	/*
 	 * Need not hold lo_ctl_mutex to fput backing file.
 	 * Calling fput holding lo_ctl_mutex triggers a circular