linux-kernel - Re: [PATCH v17 30/32] fs/resctrl: Provide interface to create architecture specific debugfs area

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Message-ID: <20260110105758.GAaWIwtlX9o_oVXIM_@fat_crate.local>
Date: Sat, 10 Jan 2026 11:57:58 +0100
From: Borislav Petkov <bp@...en8.de>
To: Tony Luck <tony.luck@...el.com>
Cc: Fenghua Yu <fenghuay@...dia.com>,
	Reinette Chatre <reinette.chatre@...el.com>,
	Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>,
	Peter Newman <peternewman@...gle.com>,
	James Morse <james.morse@....com>, Babu Moger <babu.moger@....com>,
	Drew Fustini <dfustini@...libre.com>,
	Dave Martin <Dave.Martin@....com>, Chen Yu <yu.c.chen@...el.com>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	patches@...ts.linux.dev
Subject: Re: [PATCH v17 30/32] fs/resctrl: Provide interface to create
 architecture specific debugfs area

On Wed, Dec 17, 2025 at 09:21:17AM -0800, Tony Luck wrote:
> All files below /sys/fs/resctrl are considered user ABI.
> 
> This leaves no place for architectures to provide additional interfaces.
> 
> Add resctrl_debugfs_mon_info_arch_mkdir() which creates a directory in
> the debugfs file system for a monitoring resource. Naming follows the
> layout of the main resctrl hierarchy:
> 
> 	/sys/kernel/debug/resctrl/info/{resource}_MON/{arch}
> 
> The {arch} last level directory name matches the output of the user level
> "uname -m" command.
> 
> Architecture code may use this directory for debug information, or for minor
> tuning of features. It must not be used for basic feature enabling as debugfs
> may not be configured/mounted on production systems.

I, like you guys, thought that debugfs is "safe" in the sense, stuff there
can't really be an ABI but just recently at LPC I got schooled about it and,
basically, if anything in luserspace starts using debugfs, it will be
considered an ABI.

And this thinking has been there for a looong time now:

https://lwn.net/Articles/309298/

So, before you put anything there, think again because you might end up
supporting it just like an ABI.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette