linux内核由struct file获取filename

参考：

http://stackoverflow.com/questions/17885676/in-linux-how-can-i-get-the-filename-from-the-struct-file-structure-while-ste

获取文件名:

struct file *filp with filp->f_path.dentry->d_iname.

获取全路径：

dentry_path_raw(filp->f_path.dentry,buf,buflen)