linux-kernel - Re: [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue of sysfs pagebuf

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Date:   Thu, 29 Apr 2021 07:21:13 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tian Tao <tiantao6@...ilicon.com>, corbet@....net,
        gregkh@...uxfoundation.org, song.bao.hua@...ilicon.com
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: Re: [PATCH 1/2] CPU, NUMA topology ABIs: clarify the overflow issue
 of sysfs pagebuf

On 4/29/21 12:03 AM, Tian Tao wrote:
> diff --git a/Documentation/ABI/stable/sysfs-devices-node b/Documentation/ABI/stable/sysfs-devices-node
> index 484fc04..82dfe64 100644
> --- a/Documentation/ABI/stable/sysfs-devices-node
> +++ b/Documentation/ABI/stable/sysfs-devices-node
> @@ -47,7 +47,10 @@ What:		/sys/devices/system/node/nodeX/cpulist
>  Date:		October 2002
>  Contact:	Linux Memory Management list <linux-mm@...ck.org>
>  Description:
> -		The CPUs associated to the node.
> +		The CPUs associated to the node. The format is like 0-3,
> +		8-11, 14,17. maximum size is PAGE_SIZE, so the tail
> +		of the string will be trimmed while its size is larger
> +		than PAGE_SIZE.

I think it's pretty arguable that truncating output on a real system is
an ABI break.  Doing this would make the interface rather useless.

Don't we need a real solution rather than throwing up our hands?

Do we think >PAGE_SIZE data out of a sysfs file is a worse ABI break or
something?