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

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Date:   Mon, 23 May 2022 16:58:21 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Hao Luo <haoluo@...gle.com>
Cc:     Yonghong Song <yhs@...com>, Tejun Heo <tj@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Yosry Ahmed <yosryahmed@...gle.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

On Fri, May 20, 2022 at 7:35 PM Hao Luo <haoluo@...gle.com> wrote:
>
> On Fri, May 20, 2022 at 5:59 PM Yonghong Song <yhs@...com> wrote:
> > On 5/20/22 3:57 PM, Tejun Heo wrote:
> > > 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.
> >
> > This works for me too. Thanks!
> >
>
> This sounds good to me. Thanks. Let's try to do it in the next iteration.

Can we, in addition to descendant_pre and descendant_post walk
algorithms also add the one that does ascendants walk (i.e., start
from specified cgroup and walk up to the root cgroup)? I don't have
specific example, but it seems natural to include it for "cgroup
iterator" in general. Hopefully it won't add much code to the
implementation.