linux-kernel - Re: [PATCH v1 03/31] x86/resctrl: Move ctrlval string parsing policy away from the arch code

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Date: Mon, 8 Apr 2024 20:14:47 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>
CC: Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, H Peter Anvin
	<hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
	<shameerali.kolothum.thodi@...wei.com>, D Scott Phillips OS
	<scott@...amperecomputing.com>, <carl@...amperecomputing.com>,
	<lcherian@...vell.com>, <bobo.shaobowang@...wei.com>,
	<tan.shaopeng@...itsu.com>, <baolin.wang@...ux.alibaba.com>, Jamie Iles
	<quic_jiles@...cinc.com>, Xin Hao <xhao@...ux.alibaba.com>,
	<peternewman@...gle.com>, <dfustini@...libre.com>, <amitsinght@...vell.com>,
	David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
	"Dave Martin" <dave.martin@....com>
Subject: Re: [PATCH v1 03/31] x86/resctrl: Move ctrlval string parsing policy
 away from the arch code

Hi James,

On 3/21/2024 9:50 AM, James Morse wrote:
> The policy for parsing the configuration values as a string from
> user-space is specified by a function pointer the arch code specifies.
> 
> These strings are part of resctrl's ABI, and the functions and their
> caller both live in the same file. Exporting the parsing functions and
> allowing the architecture to choose how a schema is parsed allows an
> architecture to get this wrong.
> 
> Keep this all in the flesystem parts of resctrl. This should prevent any

flesystem -> filesystem

> architecture's string-parsing behaviour from varying without core code
> changes. Use the fflags to spot caches and bandwidth resources, and use
> the appropriate helper.
> 
> Signed-off-by: James Morse <james.morse@....com>
> ---

..

> @@ -195,6 +204,14 @@ int parse_cbm(struct rdt_parse_data *data, struct resctrl_schema *s,
>  	return 0;
>  }
>  
> +static ctrlval_parser_t *get_parser(struct rdt_resource *res)
> +{
> +	if (res->fflags & RFTYPE_RES_CACHE)
> +		return &parse_cbm;
> +	else
> +		return &parse_bw;
> +}

This is borderline ... at minimum it expands what fflags means and how it
is intended to be used and that needs to be documented because it reads:

	* @fflags:		flags to choose base and info files

I am curious why you picked fflags instead of an explicit check against
rid?

Reinette