Re: userspace breakage

Linus Torvalds
2005-12-30T00:49:38Z

On Thu, 29 Dec 2005, Ryan Anderson wrote:
>
> This, for what it's worth, is the same breakage that Dave seemed to be
> most frustrated with during his OLS keynote, regarding ALSA versions,
> and a few other things that caused breakage and the user space failed to
> work correctly when the kernel was reverted. (I hope I'm not putting
> words in your mouth, Dave).

I agree: the worst part of version dependency is that it's really hard in
general to just move one of the components backwards or forwards.
Something you want to do when breakage occurs, or just because you need to
figure out some _other_ problem (like doing a kernel bug bisection).

Which is why pretty much _every_ component needs to be backwards
compatible at least to some degree. Otherwise they'd need to be bundled
and developed together as one thing.

IOW, the same way it's wrong for the kernel to need new binaries, it's
wrong for binaries to need a new kernel. It's one reason why we seldom add
new system calls: they aren't all that useful in any kind of short
timeframe, because even programs that would _like_ to use them usually
can't do so for a long time (until they don't have to worry about people
running old kernels any more).

(Some system calls are easier to add than others - if you can easily
emulate the new system call semantics with just a slight performance hit,
you can just have a simple wrapper with a fallback. That doesn't always
work well - some things are just very hard to emulate efficiently).

Linus