Subject: Re: [PATCH v2 net-next 4/4] bpftool: implement cgroup bpf operations
To: Quentin Monnet <quentin.monnet@netronome.com>,
        Roman Gushchin <guro@fb.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@fb.com, ast@kernel.org, daniel@iogearbox.net,
        jakub.kicinski@netronome.com, kafai@fb.com
References: <20171207183909.16240-1-guro@fb.com>
 <20171207183909.16240-5-guro@fb.com>
 <d3cc2f85-f3ee-7771-c5b2-13ca6e80a910@netronome.com>
 <20171208141251.GA9458@castle>
 <0eed580a-804b-329e-7bfc-1dc5c09a1deb@netronome.com>
From: David Ahern <dsahern@gmail.com>
Message-ID: <77e22817-4be2-ae4f-11b7-ebc4c51f39f3@gmail.com>
Date: Fri, 8 Dec 2017 09:52:16 -0700
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On 12/8/17 8:39 AM, Quentin Monnet wrote:
> I don't believe compatibility is an issue here, since the program and
> its documentation come together (so they should stay in sync) and are
> part of the kernel tree (so the tool should be compatible with the
> kernel sources it comes with). My concern is that there is no way to
> guess from the current description what the values for ATTACH_FLAG or
> ATTACH_TYPE can be, without reading the source code of the program—which
> is not exactly user-friendly.
> 

The tool should be backward and forward compatible across kernel
versions. Running a newer command on an older kernel should fail in a
deterministic. While the tool is in the kernel tree for ease of
development, that should not be confused with having a direct tie to any
kernel version.

I believe man pages do include kernel version descriptions in flags
(e.g., man 7 socket -- flags are denoted with "since Linux x.y") which
is one way to handle it with the usual caveat that vendors might have
backported support to earlier kernels.