The ABI status of filesystem formats

I didn't mean writing a spec is a waste of time. Specs are good because they encourage rigorous thinking. I meant it would be very difficult and a waste of time to try detect filesystems like Josh's in advance and prevent them from mounting.

But although specs have their uses, in the kernel, specs cannot work in the way you have said. The rule is never "You can't break the spec." The rule is "You can't break userspace."

Here is an example. Ten years ago glibc changed memcpy(). https://lwn.net/Articles/414467/ The spec said that the new implementation of memcpy() was valid but kernel developers find this attitude rage inducing. We would never do that in the kernel. You could theoretically still change memcpy(), but first you would have to fix all the applications that rely on the old behavior.

In the glibc example, it's not the flash developers who suffered, it's the regular Linux users. For the users, they had a program which worked and now it doesn't work. They don't care about specs. As kernel developers we care about users first and the spec second.