linux-kernel - Re: [PATCH bpf-next v9 1/5] bpf: Introduce cgroup iter

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Date:   Fri, 26 Aug 2022 19:15:29 +0200
From:   Michal Koutný <mkoutny@...e.com>
To:     Hao Luo <haoluo@...gle.com>
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        cgroups@...r.kernel.org, netdev@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        KP Singh <kpsingh@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        David Rientjes <rientjes@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Yosry Ahmed <yosryahmed@...gle.com>
Subject: Re: [PATCH bpf-next v9 1/5] bpf: Introduce cgroup iter

On Thu, Aug 25, 2022 at 10:58:26AM -0700, Hao Luo <haoluo@...gle.com> wrote:
> Permission is a valid point about FD. There was discussion in an
> earlier version of this patch series [0].

(I'm sorry, I didn't follow all the version discussions closely.)

I think the permissions are a non-issue when unprivileged BPF is
disabled. If it's allowed, I think it'd be better solved generally
within the BPF iterator framework. (Maybe it's already present, I didn't
check.)

(OT:
> The good thing about ID is that it can be passed across processes 

FDs can be passed too (parent-child trivially, others via SCM_RIGHTS
message).

> and it's meaningful to appear in logs. It's more user-friendly.

I'd say cgroup path wins both in meaning and user friendliness.
(Or maybe you meant different class of users.)
)

> So we decided to support both.

I accept cgroup ids are an establish{ing,ed} way to refer to cgroups
from userspace. Hence my fixups for the BPF cgroup iter (another thread)
for better namespacing consisntency.

Thanks,
Michal

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