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From:   Hao Luo <haoluo@google.com>
Date:   Thu, 7 Jul 2022 16:36:23 -0700
Message-ID: <CA+khW7hqVbNWFbZcJz2QWV=c5SD1ci5KOD+t4drYt2-yqpyNTg@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2 4/8] bpf: Introduce cgroup iter
To:     Yonghong Song <yhs@fb.com>
Cc:     Yosry Ahmed <yosryahmed@google.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>, Tejun Heo <tj@kernel.org>,
        Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Shuah Khan <shuah@kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        David Rientjes <rientjes@google.com>,
        Stanislav Fomichev <sdf@google.com>,
        Greg Thelen <gthelen@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
        bpf@vger.kernel.org, cgroups@vger.kernel.org
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On Mon, Jun 27, 2022 at 9:14 PM Yonghong Song <yhs@fb.com> wrote:
>
> > +static int __cgroup_iter_seq_show(struct seq_file *seq,
> > +                               struct cgroup_subsys_state *css, int in_stop)
> > +{
> > +     struct cgroup_iter_priv *p = seq->private;
> > +     struct bpf_iter__cgroup ctx;
> > +     struct bpf_iter_meta meta;
> > +     struct bpf_prog *prog;
> > +     int ret = 0;
> > +
> > +     /* cgroup is dead, skip this element */
> > +     if (css && cgroup_is_dead(css->cgroup))
> > +             return 0;
> > +
> > +     ctx.meta = &meta;
> > +     ctx.cgroup = css ? css->cgroup : NULL;
> > +     meta.seq = seq;
> > +     prog = bpf_iter_get_info(&meta, in_stop);
> > +     if (prog)
> > +             ret = bpf_iter_run_prog(prog, &ctx);
>
> Do we need to do anything special to ensure bpf program gets
> up-to-date stat from ctx.cgroup?
>

Let's leave that to be handled by bpf programs. The kfunc rstat_flush
can be called to sync stats, if using rstat.

> > +
> > +     /* if prog returns > 0, terminate after this element. */
> > +     if (ret != 0)
> > +             p->terminate = true;
> > +
> > +     return 0;
> > +}
> > +
> [...]