linux-kernel - Re: [RFC PATCH] device-core: sysfs open

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Message-ID: <1288679408.2080.18.camel@noppispoppis.nmp.nokia.com>
Date:	Tue, 02 Nov 2010 08:30:08 +0200
From:	Onkalo Samu <samu.p.onkalo@...ia.com>
To:	ext Alan Cox <alan@...ux.intel.com>
Cc:	Ming Lei <tom.leiming@...il.com>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"hmh@....eng.br" <hmh@....eng.br>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] device-core: sysfs open - close notify

On Mon, 2010-11-01 at 18:11 +0100, ext Alan Cox wrote:
> > Your patch may cause many unnecessary memory waste because
> > most of drivers does not need attribute file .open/.close notifier.
> 
> Firstly there are not that many driver objects in a small system so it
> wouldn't take that much to shift the balance the other way. Secondly
> its becoming clear that every time a driver goes to runtime pm these
> issues come up - even with things like configuration values for drivers
> that need to wake the hardware and then silence it.
> 
> So the whole sysfs/open thing is going to keep haunting us with runtime
> pm, the question is where to put the callbacks so we don't bloat stuff.
> Clearly not per attribute or per sysfs node. One possibility would be
> with the runtime pm stuff, but that would need a clean reliable way to
> go sysfs->device->runtime_pm
> 
> There are also obvious hackish ways to handle it like passing a 0
> length read to indicate close etc - they save memory but they are
> asking for problems in future.
> 

Memory footprint could be minimized by combining separate open close
functions to one like sysfs_open_close_notify and the actual operation
would be a call parameter. But is that hackish?

And perhaps some flags could be used to indicate which attributes trigs
the open / close notification.

-Samu

 


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