netdev - Re: [PATCH bpf-next v6 05/13] bpf: Add documentation for kfuncs

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Date:   Wed, 20 Jul 2022 19:03:52 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Kumar Kartikeya Dwivedi <memxor@...il.com>, bpf@...r.kernel.org
Cc:     KP Singh <kpsingh@...nel.org>, Jonathan Corbet <corbet@....net>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Florian Westphal <fw@...len.de>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>, netdev@...r.kernel.org,
        netfilter-devel@...r.kernel.org
Subject: Re: [PATCH bpf-next v6 05/13] bpf: Add documentation for kfuncs

Kumar Kartikeya Dwivedi <memxor@...il.com> writes:

> As the usage of kfuncs grows, we are starting to form consensus on the
> kinds of attributes and annotations that kfuncs can have. To better help
> developers make sense of the various options available at their disposal
> to present an unstable API to the BPF users, document the various kfunc
> flags and annotations, their expected usage, and explain the process of
> defining and registering a kfunc set.

[...]

> +2.4.2 KF_RET_NULL flag
> +----------------------
> +
> +The KF_RET_NULL flag is used to indicate that the pointer returned by the kfunc
> +may be NULL. Hence, it forces the user to do a NULL check on the pointer
> +returned from the kfunc before making use of it (dereferencing or passing to
> +another helper). This flag is often used in pairing with KF_ACQUIRE flag, but
> +both are mutually exclusive.

That last sentence is contradicting itself. "Mutually exclusive" means
"can't be used together". I think you mean "orthogonal" or something to
that effect?

-Toke