void rt_mmcsd_blk_remove(struct rt_mmcsd_card *card)
{
    rt_list_t *l, *n;
    struct mmcsd_blk_device *blk_dev;

+     if(card == RT_NULL)
+     {
+         LOG_E("card is null!");
+         return;
+     }
+
+     if(rt_list_isempty(&card->blk_devices))
+     {
+         LOG_E("card blk_devices is empty!");
+         return;
+     }
+
+     if ((&card->blk_devices)->next == RT_NULL)
+     {
+         LOG_E("card blk_devices is null!");
+         return;
+     }

    for (l = (&card->blk_devices)->next, n = l->next; l != &card->blk_devices; l = n, n=n->next)
    {
        blk_dev = (struct mmcsd_blk_device *)rt_list_entry(l, struct mmcsd_blk_device, list);
        if (blk_dev->card == card)
        {
            /* unmount file system */
            const char * mounted_path = dfs_filesystem_get_mounted_path(&(blk_dev->dev));
            if (mounted_path)
            {
                  dfs_unmount(mounted_path);
                  LOG_D("unmount file system %s for device %s.\r\n", mounted_path, blk_dev->dev.parent.name);
            }
            rt_sem_delete(blk_dev->part.lock);
            rt_device_unregister(&blk_dev->dev);
            rt_list_remove(&blk_dev->list);
            rt_free(blk_dev);
        }
    }
}