linux-kernel - Re: [PATCH v2 2/3] fs/resctrl: Return -EINVAL for a missing seq

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Message-ID: <cf6b025b-cdbf-4d15-b56d-9f8434a57da4@intel.com>
Date: Tue, 16 Dec 2025 21:02:27 -0800
From: Reinette Chatre <reinette.chatre@...el.com>
To: Aaron Tomlin <atomlin@...mlin.com>, <tony.luck@...el.com>,
	<Dave.Martin@....com>, <james.morse@....com>, <babu.moger@....com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>
CC: <sean@...e.io>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] fs/resctrl: Return -EINVAL for a missing seq_show
 implementation

Hi Aaron,

How is this change required to support the feature of enabling user to
set CBM across domains?

On 12/15/25 3:02 PM, Aaron Tomlin wrote:
> The rdtgroup_seqfile_show() function, which is the sequence file handler
> for reading data from resctrl files, previously returned 0 (success) if
> the file's associated rftype did not define a .seq_show implementation.
> 
> This behavior is incorrect and confusing, as a read operation that
> does not define a display function should be treated as an error.

Why should it be treated as an error? Not having rftype::seq_show() set when
user is intended to be able to see data when reading from the file is a kernel
bug. Otherwise it seems fine to return nothing when there is nothing to show
and doing so be successful.

Reinette