linux-kernel - Re: [PATCH bpf-next v5 00/17] Introduce eBPF support for HID devices

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Date:   Thu, 19 May 2022 01:10:48 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        Jiri Kosina <jikos@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Shuah Khan <shuah@...nel.org>,
        Dave Marchevsky <davemarchevsky@...com>,
        Joe Stringer <joe@...ium.io>, Jonathan Corbet <corbet@....net>,
        Tero Kristo <tero.kristo@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 00/17] Introduce eBPF support for HID devices

> 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.