求教vfs_readdir的有关问题

求教vfs_readdir的问题

C/C++ code

int vfs_readdir(struct file *file, filldir_t filler, void *buf){    struct inode *inode = file->f_path.dentry->d_inode;    int res = -ENOTDIR;    if (!file->f_op || !file->f_op->readdir)        goto out;    res = security_file_permission(file, MAY_READ);    if (res)        goto out;    res = mutex_lock_killable(&inode->i_mutex);    if (res)        goto out;    res = -ENOENT;    if (!IS_DEADDIR(inode)) {        res = file->f_op->readdir(file, buf, filler);        file_accessed(file);    }    mutex_unlock(&inode->i_mutex);out:    return res;}EXPORT_SYMBOL(vfs_readdir);