linux-kernel - Re: [PATCH bpf-next 0/4] Introduce bpf_kernfs_read

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Message-ID: <aFNdNv4Bvw6MwlaH@slm.duckdns.org>
Date: Wed, 18 Jun 2025 14:43:34 -1000
From: Tejun Heo <tj@...nel.org>
To: Song Liu <song@...nel.org>
Cc: bpf@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-security-module@...r.kernel.org,
	kernel-team@...a.com, andrii@...nel.org, eddyz87@...il.com,
	ast@...nel.org, daniel@...earbox.net, martin.lau@...ux.dev,
	viro@...iv.linux.org.uk, brauner@...nel.org, jack@...e.cz,
	kpsingh@...nel.org, mattbobrowski@...gle.com, amir73il@...il.com,
	gregkh@...uxfoundation.org, daan.j.demeyer@...il.com
Subject: Re: [PATCH bpf-next 0/4] Introduce bpf_kernfs_read_xattr

Hello,

On Wed, Jun 18, 2025 at 04:37:35PM -0700, Song Liu wrote:
> Introduce a new kfunc bpf_kernfs_read_xattr, which can read xattr from
> kernfs nodes (cgroupfs, for example). The primary users are LSMs, for
> example, from systemd. sched_ext could also use xattrs on cgroupfs nodes.
> However, this is not allowed yet, because bpf_kernfs_read_xattr is only
> allowed from LSM hooks. The plan is to address sched_ext later (or in a
> later revision of this set).

I don't think kernfs is the name we should be exposing to BPF users. This is
an implementation detail which may change in the future. I'd rather make it
a generic interface or a cgroup specific one. The name "kernfs" doesn't
really mean much outside kernel code that's using them.

Thanks.

-- 
tejun