linux-kernel - Re: [RFC PATCH v2 1/3] ACPI / hotplug: Send change events for offline/online requests when eject is triggered

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Message-ID: <20200313082026.GA4725@linux-8mug>
Date:   Fri, 13 Mar 2020 16:21:45 +0800
From:   Chester Lin <clin@...e.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
CC:     "lenb@...nel.org" <lenb@...nel.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "robert.moore@...el.com" <robert.moore@...el.com>,
        "erik.schmauss@...el.com" <erik.schmauss@...el.com>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Joey Lee <JLee@...e.com>,
        "mhocko@...nel.org" <mhocko@...nel.org>
Subject: Re: [RFC PATCH v2 1/3] ACPI / hotplug: Send change events for
 offline/online requests when eject is triggered

Hi Rafael,

On Wed, Jan 15, 2020 at 11:15:08AM +0100, Rafael J. Wysocki wrote:
> On Friday, January 3, 2020 5:40:09 AM CET Chester Lin wrote:
> > Here we change offline/online handling in device hotplug by sending change
> > events to userland as notification so that userland can have control and
> > determine when will be a good time to put them offline/online based on
> > current workload. In this approach the real offline/online opertions are
> > handed over to userland so that userland can have more time to prepare
> > before any device change actually happens.
> > 
> > All child devices under the ejection target are traversed and notified
> > hierarchically based on ACPI namespace in ascending order when an eject
> > event happens.
> > 
> > Signed-off-by: Chester Lin <clin@...e.com>
> 
> So you replace the old flow with the new one and make the new one mandatory AFAICS.
> 
> Thus if anyone has relied on the old flow, they now need to switch over.
> 
> This is unfriendly and generally unwelcome, so please avoid making changes like
> that.
>
Thank you for the reminder.

> Instead, I would consider adding a device attribute to allow user space to
> opt in for getting offline notifications for specific individual devices (by
> setting that attribute user space would tell the kernel that it wants to
> get offline notifications for the device in question and it would take
> care of offlining it as needed).
> 
Thanks for your advice. If no one is working on this device attribute [please free
feel to correct me if I'm wrong], I am willing to implement it and will send a new
RFC patch for code review.

Regards,
Chester