linux-kernel - RE: [PATCH] sysfs: Remove page boundary align limitation on sysfs_emit and sysfs_emit

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Date:   Thu, 9 Sep 2021 05:27:49 +0000
From:   "Yu, Lang" <Lang.Yu@....com>
To:     Joe Perches <joe@...ches.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] sysfs: Remove page boundary align limitation on
 sysfs_emit and sysfs_emit_at

[AMD Official Use Only]



>-----Original Message-----
>From: Joe Perches <joe@...ches.com>
>Sent: Thursday, September 9, 2021 1:06 PM
>To: Yu, Lang <Lang.Yu@....com>; Greg Kroah-Hartman
><gregkh@...uxfoundation.org>; Rafael J . Wysocki <rafael@...nel.org>; linux-
>kernel@...r.kernel.org
>Subject: Re: [PATCH] sysfs: Remove page boundary align limitation on sysfs_emit
>and sysfs_emit_at
>
>On Wed, 2021-09-08 at 20:07 +0800, Lang Yu wrote:
>> The key purpose of sysfs_emit and sysfs_emit_at is to ensure that no
>> overrun is done. Make them more equivalent with scnprintf.
>
>I can't think of a single reason to do this.
>sysfs_emit and sysfs_emit_at are specific to sysfs.
>
>Use of these functions outside of sysfs is not desired or supported.
>
>
Thanks for your reply. But I'm still curious why you put such a limitation.
As "Documentation/filesystems/sysfs.rst" described, we can just  use 
scnprintf(buf, PAGE_SIZE, "%s\n", dev->name) in show functions without
such a limitation.

But you said that " - show() should only use sysfs_emit() or sysfs_emit_at() when formatting
the value to be returned to user space. " in Documentation/filesystems/sysfs.rst.

Some guys just try to replace scnprintf with sysfs_emit() or sysfs_emit_at() per above documents.
But sprintf and sysfs_emit/sysfs_emit_at are not totally equivalent(e.g., page boundary align).

In my opinion, we add a new api and try to replace an old api. Does we need to make it more
compatible with old api? Thanks.

Regards,
Lang