Re: [PATCH v2 net-next 4/4] bpftool: implement cgroup bpf operations

[David Ahern <dsahern@gmail.com>]

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.