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

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Message-ID: <5b301151-0a65-df43-3a3a-6d57e10cfc2d@fb.com>
Date:   Fri, 20 May 2022 17:59:21 -0700
From:   Yonghong Song <yhs@...com>
To:     Tejun Heo <tj@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>, Hao Luo <haoluo@...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 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!

> 
> Thanks.
>