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Date:   Thu, 19 May 2022 01:10:48 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc:     Greg KH <gregkh@linuxfoundation.org>,
        Jiri Kosina <jikos@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>, Shuah Khan <shuah@kernel.org>,
        Dave Marchevsky <davemarchevsky@fb.com>,
        Joe Stringer <joe@cilium.io>, Jonathan Corbet <corbet@lwn.net>,
        Tero Kristo <tero.kristo@linux.intel.com>,
        linux-kernel@vger.kernel.org, linux-input@vger.kernel.org,
        netdev@vger.kernel.org, bpf@vger.kernel.org,
        linux-kselftest@vger.kernel.org, linux-doc@vger.kernel.org
Subject: Re: [PATCH bpf-next v5 00/17] Introduce eBPF support for HID devices
Message-ID: <YoX7iHddAd4FkQRQ@infradead.org>
References: <20220518205924.399291-1-benjamin.tissoires@redhat.com>
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In-Reply-To: <20220518205924.399291-1-benjamin.tissoires@redhat.com>
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> The logic is the following (see also the last patch for some more
> documentation):
> - hid-bpf first preloads a BPF program in the kernel that does a few
>   things:
>    * find out which attach_btf_id are associated with our trace points
>    * adds a bpf_tail_call() BPF program that I can use to "call" any
>      other BPF program stored into a jump table
>    * monitors the releases of struct bpf_prog, and when there are no
>      other users than us, detach the bpf progs from the HID devices
> - users then declare their tracepoints and then call
>   hid_bpf_attach_prog() in a SEC("syscall") program
> - hid-bpf then calls multiple time the bpf_tail_call() program with a
>   different index in the jump table whenever there is an event coming
>   from a matching HID device

So driver abstractions like UDI are now perfectly fine as long as they
are written using a hip new VM?

This whole idea seems like a bad idea, against the Linux spirit and
now actually useful - it is totally trivial to write a new HID
driver alreay, and if it isn't in some cases we need to fix that.

So a big fat NAK to the idea of using eBPF for actual driver logic.