Never break userspace [LWN.net]

Never break userspace

Posted Feb 16, 2024 19:10 UTC (Fri) by mb (subscriber, #50428)
In reply to: Never break userspace by rahulsundaram
Parent article: A turning point for CVE numbers

>The difference is that kernel developers have publicly committed to never breaking userspace

Things like uevents, tracepoints, sysfs files, etc... were pretty much never part of that claim.
Devs try hard to not make unnecessary breakages, but if a sysfs file disappears/changes or an uevent changes, programs have to deal with it.
Has always been like that.

> It is the disconnect between the public messaging and reality that's causing the contention.

The disconnect between the expectation and the reality is causing the contention.

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Never break userspace

Posted Feb 16, 2024 19:21 UTC (Fri) by bluca (subscriber, #118303) [Link] (2 responses)

> Things like uevents, tracepoints, sysfs files, etc... were pretty much never part of that claim.

Citation needed. That is very much not evident from any claim anybody has ever made that I have seen.

Never break userspace

Posted Feb 16, 2024 19:41 UTC (Fri) by mb (subscriber, #50428) [Link] (1 responses)

>Citation needed

Even syscalls have been removed in the past, breaking applications.
BUT these applications always were very limited in count and usually part of the OS itself.

Citation: Look at the sources.

There has never been a thing like a general stability guarantee.
It always has been a matter of common sense.
If a change only breaks udev or systemd and nothing else, it might make sense to do it.

Never break userspace

Posted Feb 16, 2024 20:07 UTC (Fri) by bluca (subscriber, #118303) [Link]

Excellent, you have now demonstrated that my original post, claiming that there is no such thing as 'kernel never breaks userspace', was indeed correct, and thus 'just update to the latest' cannot be suggested as a solution to security issues since public interfaces will be broken left and right with no regard for backward compatibility. Congrats!

> If a change only breaks udev or systemd and nothing else, it might make sense to do it.

I beg to differ