Documentation/ABI/README doesn't list an "experimental" level of
stability. I suppose a developer with an API they expect to change could
create it as "obsolete" (since the experimental verison will get removed
when the real one is done), but that's a little odd as a use of that
category. Also, that doesn't stop people from looking through sysfs for
useful stuff they expect to be undocumented but easy enough to figure out,
and starting to use it without realizing that it's not intended to be
maintained. And the "stable/syscalls" entry implies that all syscalls are
stable when they get merged, which means that a patch that adds a syscall
can't stablize in mainline.
If there are people, like the Nouveau developers, using the instability of
their userspace API as a reason not to submit their drivers, and we would
ideally like the drivers to stabilize with mainline exposure, then we need
to do something more to address these authors' concerns.
-Daniel
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