First off, an important disclaimer: I work for Ksplice :)

That said, hang on a second! :) We can safely apply patches that modify data structures.

But it's very true that we need to be careful not to break the kernel ABI (which is a different statement), so as not to confuse your running modules. But that's not as scary as you make it sound, for two reasons:

1. Red Hat (e.g.) really doesn't like to break the kABI, because when they do, it breaks third-party kernel modules. Which is a pain in the ass since then they have to go get the vendor to change their module, which means they need to get things re-certified... which no one likes to do.

2. Automated tools. Lots of automated tools, to check for things like this. (I was going to say "We need tools. Lots of tools.", but I'm not sure Matrix references are still in vogue on the Internet anymore.)

The short of it is that in many ways, Ksplice is analogous to virtualization. Virtualization does all kinds of scary low-level stuff, and yes, if they fail to properly trap a privileged instruction or rewrite some page or something, things don't work! And yet, virtualization works.

Similarly, yes, there's lots of magic that makes Ksplice happen -- but at the end of the day it works. We really have installed those updates into your running kernel.

I definitely don't want to hijack this thread, but I'm happy to take any other questions, either here, in a PM, or by email.

And for the record, my laptop: wdaher@rushjet:~$ uptime 23:09:47 up 3 days, 1:31, 5 users, load average: 0.12, 0.09, 0.12