linux-kernel - Re: [RFC PATCH bpf-next 0/3] bpf: freeze a task cgroup from bpf

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Date: Thu, 28 Mar 2024 13:23:22 -1000
From: Tejun Heo <tj@...nel.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Djalal Harouni <tixxdz@...il.com>, Zefan Li <lizefan.x@...edance.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
	bpf <bpf@...r.kernel.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" <linux-kselftest@...r.kernel.org>
Subject: Re: [RFC PATCH bpf-next 0/3] bpf: freeze a task cgroup from bpf

Hello,

On Thu, Mar 28, 2024 at 02:28:51PM -0700, Alexei Starovoitov wrote:
> > > So filename will be one of cgroup_base_files[].name ?
> > > We probably don't want psi or cgroup1_base_files in there.
> >
> > Would it matter?
> 
> Few weak reasons:
> . cgroup_psi_files have show/write/poll/release which
>   doesn't map to this bpf_cgroup_knob_write/read ?
> . cgroup1_base_files probably needs to a separate kfunc
>   bpf_cgroup1_...
> 
> > If the user has root perm, they can do whatever with the
> > files anyway, so I'm not sure why we'd restrict any specific knob. Maybe we
> > wanna make sure @filename doesn't include '/'? Or is it that you don't want
> > to go through the usual file name look up?
> 
> yeah. why do a file lookup? The names are there in the array.
> cgroup pointer gives that "relative path" and knob name is the last
> part of such "path". Easy to search in that array(s).

Difficult to tell without looking at the implementation but I don't have
strong opinions. The interface makes sense to me and as long as we can hook
it up in a reasonably way, it should be okay. We can always change internal
implementation later if necessary.

Thanks.

-- 
tejun