netdev - Re: [PATCH RFC 2/3] bpf: set attached cgroup name in attach

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Date:   Sat, 19 Feb 2022 10:27:15 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH RFC 2/3] bpf: set attached cgroup name in attach_name

On Fri, Feb 18, 2022 at 1:56 AM Yafang Shao <laoar.shao@...il.com> wrote:
>
> Set the cgroup path when a bpf prog is attached to a cgroup, and unset
> it when the bpf prog is detached.
>
> Below is the result after this change,
> $ cat progs.debug
>   id name             attached
>    5 dump_bpf_map     bpf_iter_bpf_map
>    7 dump_bpf_prog    bpf_iter_bpf_prog
>   17 bpf_sockmap      cgroup:/
>   19 bpf_redir_proxy
>
> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> ---
>  kernel/bpf/cgroup.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 43eb3501721b..ebd87e54f2d0 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -440,6 +440,7 @@ static int __cgroup_bpf_attach(struct cgroup *cgrp,
>         struct bpf_cgroup_storage *storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
>         struct bpf_cgroup_storage *new_storage[MAX_BPF_CGROUP_STORAGE_TYPE] = {};
>         enum cgroup_bpf_attach_type atype;
> +       char cgrp_path[64] = "cgroup:";
>         struct bpf_prog_list *pl;
>         struct list_head *progs;
>         int err;
> @@ -508,6 +509,11 @@ static int __cgroup_bpf_attach(struct cgroup *cgrp,
>         else
>                 static_branch_inc(&cgroup_bpf_enabled_key[atype]);
>         bpf_cgroup_storages_link(new_storage, cgrp, type);
> +
> +       cgroup_name(cgrp, cgrp_path + strlen("cgroup:"), 64);
> +       cgrp_path[63] = '\0';
> +       prog->aux->attach_name = kstrdup(cgrp_path, GFP_KERNEL);
> +

This is pure debug code. We cannot have it in the kernel.
Not even under #ifdef.

Please do such debug code on a side as your own bpf program.
For example by kprobe-ing in this function and keeping the path
in a bpf map or send it to user space via ringbuf.
Or enable cgroup tracepoint and monitor cgroup_mkdir with full path.
Record it in user space or in bpf map, etc.

Also please read Documentation/bpf/bpf_devel_QA.rst
bpf patches should be based on bpf-next tree.
These patches are not.