[k4st]

I'm trying to solve a few related high-level problems. One, is that I want Valgrind-like debugging for the kernel. In my last kernel DBT system, I was able to do some pretty neat things, but actually using the DBT system was hell. A lot of this had to do with some of my poor design decisions (e.g. quick hacks that revealed interesting research areas, but were never refactored into good code).

Another problem that I want to solve is turn on/off pervasive profiling. This will sound similar to kprobes / systemtap / dtrace / etc, but what I want you to think about is something like "tainting" some objects (like injecting radioactive die) and then being able to observe their entire lifetime. I want to make it easy for someone without 1) domain specific knowledge of parts of the kernel, and 2) the ability to change the kernel source code to be able to answer the following types of questions: "if I write some data to a socket, how long does it take that data to go out over the wire, where are hold ups, etc."

Specifically for DBT, you hit the nail on the head: I am patching jumps in the code cache to point to other blocks in the code cache. Your suggestion is analogous to a copy-on-write tree/graph. I will have to think more on it, as it is interesting.

If you're curious about my project, then feel free to reach out to me :-) My email is on my HN profile.