How to dealwith mmap for a filesystem filter driver?

Hello all, I created a filter driver for the vfs, for some special file read, I want to replace its data got from the disk and return to the new data to user space, eg. decryption. my hooked read entry like this: int my_hooked_read(struct file* filp, char* buffer, size_t count, loff_t* pos) { int ret = orig_read(filp, buffer, count, pos); if(ret > 0) { //do something } return ret; } the code works file for normal read, but take no sense for read via mmap operations. so, I want to know what should I do to resolve such issue? Thanks.