sysfs_lookup
dentry->d_op = &sysfs_dentry_ops;
dentry->d_fsdata = sysfs_get(sd);
static int sysfs_open_file(struct inode *inode, struct file *file)
struct sysfs_dirent *attr_sd = file->f_path.dentry->d_fsdata;
struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
https://www.ibm.com/developerworks/cn/linux/l-cn-sysfs