linux-kernel - Re: [PATCH bpf-next v1 3/5] bpf: Introduce cgroup iter

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Date:   Fri, 20 May 2022 12:57:20 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>, Hao Luo <haoluo@...gle.com>,
        Yonghong Song <yhs@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Michal Hocko <mhocko@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>
Subject: Re: [PATCH bpf-next v1 3/5] bpf: Introduce cgroup iter

Hello,

On Fri, May 20, 2022 at 03:19:19PM -0700, Alexei Starovoitov wrote:
> We have bpf_map iterator that walks all bpf maps.
> When map iterator is parametrized with map_fd the iterator walks
> all elements of that map.
> cgroup iterator should have similar semantics.
> When non-parameterized it will walk all cgroups and their descendent
> depth first way. I believe that's what Yonghong is proposing.
> When parametrized it will start from that particular cgroup and
> walk all descendant of that cgroup only.
> The bpf prog can stop the iteration right away with ret 1.
> Maybe we can add two parameters. One -> cgroup_fd to use and another ->
> the order of iteration css_for_each_descendant_pre vs _post.
> wdyt?

Sounds perfectly reasonable to me.

Thanks.

-- 
tejun