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From:   Daniel Colascione <dancol@google.com>
Date:   Mon, 30 Jul 2018 17:33:39 -0700
Message-ID: <CAKOZuesNnY8oKimMk+gnUppMgZt92F+razSZCSfHu=xfq+snGg@mail.gmail.com>
Subject: Re: [PATCH v3] Add BPF_SYNCHRONIZE_MAP_TO_MAP_REFERENCES bpf(2) command
To:     Jakub Kicinski <jakub.kicinski@netronome.com>
Cc:     Daniel Borkmann <daniel@iogearbox.net>,
        Joel Fernandes <joelaf@google.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Tim Murray <timmurray@google.com>,
        netdev <netdev@vger.kernel.org>,
        Alexei Starovoitov <alexei.starovoitov@gmail.com>,
        Lorenzo Colitti <lorenzo@google.com>,
        Chenbo Feng <fengc@google.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        Alexei Starovoitov <ast@fb.com>
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On Mon, Jul 30, 2018 at 5:26 PM, Jakub Kicinski
<jakub.kicinski@netronome.com> wrote:
>
> On Mon, 30 Jul 2018 03:25:43 -0700, Daniel Colascione wrote:
> > On Mon, Jul 30, 2018 at 3:04 AM, Daniel Borkmann <daniel@iogearbox.net> wrote:
> > > Hmm, I don't think such UAPI as above is future-proof. In case we would want
> > > a similar mechanism in future for other maps, we would need a whole new bpf
> > > command or reuse BPF_SYNCHRONIZE_MAP_TO_MAP_REFERENCES as a workaround though
> > > the underlying map may not even be a map-to-map. Additionally, we don't have
> > > any map object at hand in the above, so we couldn't make any finer grained
> > > decisions either. Something like below would be more suitable and leaves room
> > > for extending this further in future.
> >
> > YAGNI.  Your proposed mechanism doesn't add anything under the current
> > implementation.
>
> FWIW in case of HW offload targeting a particular map may allow users
> to avoid a potentially slow sync with all the devices on the system.


Sure. But such a thing doesn't exist right now (right?), and we can
add that more-efficient-in-that-one-case BPF interface when it lands.
I'd rather keep things simple for now.