so i have a bunch of files, some can be up to 30-40mb and i want to use php to handle security of the files, so i can control who has access to them

that means i have a script sort of like this rough example

$has_permission = check_database_for_permission($user, filename);

if ($has_permission) {
   header('Content-Type: image/jpeg'); 
   readfile ($filename);    
   exit; 
} else {
  // return 401 error
}

i would hate for every request to load the full file into memory, as it would soon chew up all the memory on my server with a few simultaneous requests

so a couple of questions

1. is readfile the most memory efficient way of doing this?
2. is there some better method of achieving the same outcome, that i am overlooking?

server: apache/php5

thanks