Linux 1.0 kernel source reading - 4: The rest of kernel/

This time, I'm polishing off the rest of the "kernel/" directory. It's a short review of a few relatively long files (not long in absolute terms, fortunately).

sys.c: vm86 is messy. I'm starting to wonder if the whole threading thing being written as a co-routine or continuation-based abstraction could hide the grim, but I'm not convinced. A lot of this file consists of very boring system calls.

fork.c: Quite fun! How to duplicate all the things you need to create an identical process. Some parts, that depend upon fs and mm aren't clear yet, as I need to read the code, but the intuition is pretty clear. I see this common pattern with C code that I get twitchy about invariants being held that would be managed wonderfully with well-encapsulated objects and RAII.

signal.c: Oh look, yet another structure to hold all the register state! This is used when saving state on the stack during signals for iBCS compatibility, it seems. The manipulation of the user stack, with the use of the "sigreturn" system call at the end of the signal handler is interesting, as is the setting up of a chain of signal handlers in a single go.

exit.c: Almost a misnomer - there's plenty of code that isn't pure exit code, as it segues to exit code handling, wait, process groups, and other signal-related stuff. Again, RAII would make safe clean-up a lot easier IMHO.

ptrace.c: Handles process debugging stuff, and is a little odd and encapsulation-breaking - it manually traverses the page table, for example.

Posted 2015-04-01.