netdev - Re: [PATCH bpf-next v5 4/8] bpf: Introduce cgroup iter

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Message-ID: <YuK+eg3lgwJ2CJnJ@slm.duckdns.org>
Date:   Thu, 28 Jul 2022 06:51:06 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Yosry Ahmed <yosryahmed@...gle.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>,
        Hao Luo <haoluo@...gle.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        KP Singh <kpsingh@...nel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Michal Koutný <mkoutny@...e.com>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        David Rientjes <rientjes@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 4/8] bpf: Introduce cgroup iter

Hello,

On Fri, Jul 22, 2022 at 05:48:25PM +0000, Yosry Ahmed wrote:
> +
> +	/* cgroup_iter walks either the live descendants of a cgroup subtree, or the
> +	 * ancestors of a given cgroup.
> +	 */
> +	struct {
> +		/* Cgroup file descriptor. This is root of the subtree if walking
> +		 * descendants; it's the starting cgroup if walking the ancestors.
> +		 * If it is left 0, the traversal starts from the default cgroup v2
> +		 * root. For walking v1 hierarchy, one should always explicitly
> +		 * specify the cgroup_fd.
> +		 */
> +		__u32	cgroup_fd;

So, we're identifying the starting point with an fd.

> +		__u32	traversal_order;
> +	} cgroup;
>  };
>  
>  /* BPF syscall commands, see bpf(2) man-page for more details. */
> @@ -6136,6 +6156,16 @@ struct bpf_link_info {
>  					__u32 map_id;
>  				} map;
>  			};
> +			union {
> +				struct {
> +					__u64 cgroup_id;
> +					__u32 traversal_order;
> +				} cgroup;

but iterating the IDs. IDs are the better choice for cgroup2 as there's
nothing specific to the calling program or the fds it has, but I guess this
is because you want to use it for cgroup1, right? Oh well, that's okay I
guess.

Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun