linux-kernel - Re: [PATCH] ACPI / Battery: Return -ENODATA for unknown values in get

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Message-Id: <201010212157.47952.rjw@sisk.pl>
Date:	Thu, 21 Oct 2010 21:57:47 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Sitsofe Wheeler <sitsofe@...oo.com>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Len Brown <lenb@...nel.org>, Zhang Rui <rui.zhang@...el.com>,
	David Zeuthen <davidz@...hat.com>,
	Richard Hughes <richard@...hsie.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ACPI / Battery: Return -ENODATA for unknown values in get_property()

On Thursday, October 21, 2010, Sitsofe Wheeler wrote:
> On Sun, Oct 17, 2010 at 08:32:42PM +0200, Rafael J. Wysocki wrote:
> > 
> > Still, if user space has problems with failing reads from the sysfs
> > attributes, it may be better to simply put -1 in there.  Patch is
> > appended, please test.
> 
> This patch does what it says on the tin (returns -1 in sysfs on my EeePC
> 900). So:
> 
> Tested-by: Sitsofe Wheeler <sitsofe@...oo.com>
> 
> It's a shame the previous changes didn't work as they stopped a buggy
> upower using the -1 value (and producing a nonsense rate like 8.4e-06)

Hmm.  So upower _doesn't_ handle -1?  What does it do with -1000, then?

> but it's not clear which part of the stack can't handle -ENODATA
> perhaps it is another part of the kernel?

I don't really think it's a part of the kernel.

> Richard, any chance of upower being changed to test for -1 before doing
> doing anything with current_now (
> http://cgit.freedesktop.org/DeviceKit/upower/tree/src/linux/up-device-supply.c?id=5387183d53c16a987a0737c1bdec1b62edf3daa6#n561)?
> I guess there are a whole bunch of other attributes that could
> theoretically be -1 and shouldn't be used if they return it...

If user space doesn't handle -1 correctly too, I think the right approach for
us should be to use the previous version of the patch and return error code
for unknown values.

Thanks,
Rafael
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