netdev - Re: [PATCH bpf-next] bpf: remove useless version check for prog load

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Message-ID: <73da8b9f-133e-ee59-b8f5-740bfa083f8f@netronome.com>
Date:   Mon, 17 Dec 2018 09:39:47 +0000
From:   Quentin Monnet <quentin.monnet@...ronome.com>
To:     Daniel Borkmann <daniel@...earbox.net>, ast@...nel.org
Cc:     yhs@...com, kafai@...com, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: remove useless version check for prog load

2018-12-16 00:49 UTC+0100 ~ Daniel Borkmann <daniel@...earbox.net>
> Existing libraries and tracing frameworks work around this kernel
> version check by automatically deriving the kernel version from
> uname(3) or similar such that the user does not need to do it
> manually; these workarounds also make the version check useless
> at the same time.
> 
> Moreover, most other BPF tracing types enabling bpf_probe_read()-like
> functionality have /not/ adapted this check, and in general these
> days it is well understood anyway that all the tracing programs are
> not stable with regards to future kernels as kernel internal data
> structures are subject to change from release to release.
> 
> Back at last netconf we discussed [0] and agreed to remove this
> check from bpf_prog_load() and instead document it here in the uapi
> header that there is no such guarantee for stable API for these
> programs.
> 
>    [0] http://vger.kernel.org/netconf2018_files/DanielBorkmann_netconf2018.pdf
> 
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Acked-by: Alexei Starovoitov <ast@...nel.org>

For what it's worth,

Acked-by: Quentin Monnet <quentin.monnet@...ronome.com>

Note: samples and selftests setting a kern_version can probably wait 
before being updated (if they get updated at all), but you might want to 
change now the remark in Documentation/bpf/bpf_design_QA.rst about 
kern_version being checked.