[LSF/MM/BPF TOPIC] Per-arg kfunc flags

[David Vernet <void@manifault.com>]

Hi all,

I would like to discuss how to enable per-arg kfunc flags.

As described in [0], kfunc flags are currently at the granularity of the
entire kfunc. This means that, for example, only a single kfunc argument
can be acquired (indicated by KF_ACQUIRE), released (indicated by
KF_RELEASE), RCU-protected (KF_RCU), etc.

This hasn't really been a problem up to this point, though there are
some per-arg annotations such as those described in [1], and patches
here and there such as [2], which collectively indicate that it may be
time to start aligning on what the design and implemention should look
like (e.g. should we model the UX for defining kfuncs in a similar to
way to helpers, go in a different direction, what blockers are there,
etc).

[0]: https://docs.kernel.org/bpf/kfuncs.html#annotating-kfuncs
[1]: https://docs.kernel.org/bpf/kfuncs.html#annotating-kfunc-parameters
[2]: https://lore.kernel.org/bpf/20221217082506.1570898-2-davemarchevsky@fb.com/

What do you all think?

Thanks,
David