linux-kernel - Re: [PATCH] [RFC] Add support for uevents on block device idle changes

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Message-ID: <ac3eb2510911190634m20947c86w78340d22eff290ca@mail.gmail.com>
Date:	Thu, 19 Nov 2009 15:34:53 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	David Zeuthen <david@...ar.dk>, linux-kernel@...r.kernel.org,
	axboe@...nel.dk, linux-hotplug@...r.kernel.org
Subject: Re: [PATCH] [RFC] Add support for uevents on block device idle 
	changes

On Thu, Nov 19, 2009 at 15:30, Matthew Garrett <mjg59@...f.ucam.org> wrote:
> On Thu, Nov 19, 2009 at 03:25:59PM +0100, Kay Sievers wrote:
>> On Thu, Nov 19, 2009 at 15:16, Matthew Garrett <mjg59@...f.ucam.org> wrote:
>> > It could, but it seems a bit of a hack. It'd still also require the
>> > timer to be in the kernel, so we might as well expose that to userspace.
>>
>> Sure, but a userspace configurable policy for an in-kernel disk-idle
>> powermanagent sounds fine, compared to a single-subscriber
>> userspace-only disk-idle event interface. :)
>
> Well, we still need to expose this for the access pattern modifying. I
> really don't see the issue with the single subscriber being devkit-disks
> - none of the operations involved are atomic, so we're inherently racy
> here.

Single-subscriber event interfaces are usually a no-go for generic
infrastructure like this. We still have the unmodified HAL running
until it is dead, and this works only because there are no such
awkward interfaces. In a few years we will probably have diskfoo
replacing dk-disks, and then ... :)

Kay
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