linux-kernel - Re: [PATCH] [RFC] bpf: tracing: new helper bpf_get_current_cgroup

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Message-ID: <20180521162609.lpdrnozowmzdn57m@ast-mbp.dhcp.thefacebook.com>
Date:   Mon, 21 May 2018 09:26:11 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Alban Crequy <alban.crequy@...il.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        containers@...ts.linux-foundation.org, cgroups@...r.kernel.org,
        Alban Crequy <alban@...volk.io>, tj@...nel.org
Subject: Re: [PATCH] [RFC] bpf: tracing: new helper bpf_get_current_cgroup_ino

On Sun, May 13, 2018 at 07:33:18PM +0200, Alban Crequy wrote:
>  
> +BPF_CALL_2(bpf_get_current_cgroup_ino, u32, hierarchy, u64, flags)
> +{
> +	// TODO: pick the correct hierarchy instead of the mem controller
> +	struct cgroup *cgrp = task_cgroup(current, memory_cgrp_id);
> +
> +	if (unlikely(!cgrp))
> +		return -EINVAL;
> +	if (unlikely(hierarchy))
> +		return -EINVAL;
> +	if (unlikely(flags))
> +		return -EINVAL;
> +
> +	return cgrp->kn->id.ino;

ino only is not enough to identify cgroup. It needs generation number too.
I don't quite see how hierarchy and flags can be used in the future.
Also why limit it to memcg?

How about something like this instead:

BPF_CALL_2(bpf_get_current_cgroup_id)
{
        struct cgroup *cgrp = task_dfl_cgroup(current);

        return cgrp->kn->id.id;
}
The user space can use fhandle api to get the same 64-bit id.