Automatically adjusting process priorities under Linux

Question

I'm trying to write a program that automatically sets process priorities based on a configuration file (basically path - priority pairs).

I thought the best solution would be a kernel module that replaces the execve() system call. Too bad, the system call table isn't exported in kernel versions > 2.6.0, so it's not possible to replace system calls without really ugly hacks.

I do not want to do the following:

-Replace binaries with shell scripts, that start and renice the binaries. -Patch/recompile my stock Ubuntu kernel -Do ugly hacks like reading kernel executable memory and guessing the syscall table location -Polling of running processes

I really want to be:

-Able to control the priority of any process based on it's executable path, and a configuration file. Rules apply to any user.

Does anyone of you have any ideas on how to complete this task?

Answer 1

There's another point of attack you might consider: replace the system's dynamic linker with a modified one which applies your logic. (See this paper for some nice examples of what's possible from the largely neglected art of linker hacking).

Where this approach will have problems is with purely statically linked binaries. I doubt there's much on a modern system which actually doesn't link something dynamically (things like busybox-static being the obvious exceptions, although you might regard the ability to get a minimal shell outside of your controls as a feature when it all goes horribly wrong), so this may not be a big deal. On the other hand, if the priority policies are intended to bring some order to an overloaded shared multi-user system then you might see smart users preparing static-linked versions of apps to avoid linker-imposed priorities.