Hi list, I am a newbie in linux kernel programming. Recently I got stuck in a problem when doing practice in file system programming. I hope this list is the right place I can turn to. I want to replace some file operations of files in a certain directory,so that data can be decrypted/encrypted through read/write system call. So I: #1: Find the directory inode, save its original inode operation table,then replace the table: kern_path(pathname, LOOKUP_FOLLOW, &target_dir_path); lower_iops = target_dir_path.dentry->d_inode->i_op; target_dir_path.dentry->d_inode->i_op = &my_iops; #2: In my_iops, I mainly changed ".lookup" function like this to achive my goal －－ replace the file operation table of all files in the directory. static struct dentry *my_inode_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd) { struct dentry *ret_dentry; ret_dentry = lower_iops->lookup(dir,dentry,nd); if (!ret_dentry) goto out; ret_dentry->d_inode->i_fop = &my_fops; out: return ret_dentry; } Things turns out that replacement of inode operation table of directory is successful but the changes in file operations are not functional: system works as it used to, totally ignore my_fops! I have no idea how to fix it. Can anybody help? Thanks for your attention! Regards Freeman Zhang