The server chose violence

I’m continuing to reflect on the past four years with Hubris — April Fool’s Day was, appropriately enough, the fourth anniversary of the first Hubris user program, and today is the fourth anniversary of the first kernel code. (I wrote the user program first to help me understand what the kernel’s API wanted to look like.)

Of all of Hubris’s design decisions, there’s one that gets a “wait what” response more often than any other. It’s also proving to be a critical part of the system’s overall robustness. In this post, I’ll take a look at our 13th and oddest syscall, REPLY_FAULT.

Who killed the network switch?

We found a neat bug in Hubris this week. Like many bugs, it wasn’t a bug when it was originally written — correct code became a bug as other things changed around it.

I thought the bug itself, and the process of finding and fixing it, provided an interesting window into our development process around Hubris. It’s very rare for us to find a bug in the Hubris kernel, mostly because it’s so small. So I jumped at the opportunity to write this one down.

This is a tale of how two features, each useful on its own, can combine to become a bug. Read on for details.

Project Loon

While I’ve been blogging about my personal projects off and on, I’ve been awfully quiet about my day job. Now I can tell you why.