linux-kernel - Re: [RFC] power/hibernate: Make passing hibernate offsets more friendly

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Date:   Fri, 2 Mar 2018 10:42:40 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Mario Limonciello <Mario.Limonciello@...l.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] power/hibernate: Make passing hibernate offsets more friendly

On Wed, Feb 28, 2018 at 9:05 PM,  <Mario.Limonciello@...l.com> wrote:
>
>
>> -----Original Message-----
>> From: Andy Shevchenko [mailto:andy.shevchenko@...il.com]
>> Sent: Wednesday, February 28, 2018 12:11 PM
>> To: Limonciello, Mario <Mario_Limonciello@...l.com>
>> Cc: Rafael J . Wysocki <rjw@...ysocki.net>; ACPI Devel Maling List <linux-
>> acpi@...r.kernel.org>; LKML <linux-kernel@...r.kernel.org>
>> Subject: Re: [RFC] power/hibernate: Make passing hibernate offsets more friendly
>>
>> On Wed, Feb 28, 2018 at 7:43 PM, Mario Limonciello
>> <mario.limonciello@...l.com> wrote:
>> > Currently the only way to specify a hibernate offset for a swap
>> > file is on the kernel command line.
>> >
>> > This makes some changes to improve:
>> > 1) Add a new /sys/power/disk_offset that lets userspace specify
>> > the offset and disk to use when initiating a hibernate cycle.
>> >
>> > 2) Adjust /sys/power/resume interpretation to also read in an
>> > offset.
>>
>> Read is okay per se (not consistent though), showing is not.
>> It might break an ABI.
>
> Right this is part of why I was proposing making a new attribute.
>
> The current RFC implementation I sent keeps the read output the
> same for /sys/power/resume.

You also need to retain the write behavior of it.

A new attribute is fine if it helps, but the behavior of the existing
one cannot change (both sides).