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Open Source and information security mailing list archives
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Date: Thu, 3 Sep 2009 23:10:43 +0200 From: "Rafael J. Wysocki" <rjw@...k.pl> To: Pavel Machek <pavel@....cz> Cc: Zhang Rui <rui.zhang@...el.com>, Len Brown <lenb@...nel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "linux-acpi" <linux-acpi@...r.kernel.org>, Greg KH <greg@...ah.com> Subject: Re: [PATCH V6 1/2] introduce ALS sysfs class On Thursday 03 September 2009, Pavel Machek wrote: > On Thu 2009-09-03 02:16:04, Rafael J. Wysocki wrote: > > On Wednesday 02 September 2009, Pavel Machek wrote: > > > On Wed 2009-09-02 23:46:11, Rafael J. Wysocki wrote: > > > > On Wednesday 02 September 2009, Pavel Machek wrote: > > > > > On Wed 2009-09-02 23:12:58, Rafael J. Wysocki wrote: > > > > > > On Tuesday 01 September 2009, Pavel Machek wrote: > > > > > > > > > > > > > > > > > IMO, 0 and -1 are not errors. they just suggest that the Ambient Light > > > > > > > > > > illuminance is beyond the device support range, while the device is > > > > > > > > > > still working normally. > > > > > > > > > > what about exporting these values (0 and -1) to user space directly? > > > > > > > > > > > > > > > > > > Returning 0 for "below" range and 99999999 for "above" range would be > > > > > > > > > nice, yes. > > > > > > > > > > > > > > > > Why not 0 and "all ones" or 0 and -1. > > > > > > > > > > > > > > > > Is there anything wrong with -1 in particular? > > > > > > > > > > > > > > Normal people expect -1 to be less than 123, and output is in ascii. If > > > > > > > you make it ((unsigned) ~0) I guess that becomes acceptable. > > > > > > > > > > > > Well, "-1" is a perfectly valid alphanumerical representation of an int. > > > > > > I don't really see the problem with the "-", unless we're talking about some > > > > > > broken user space, that is. > > > > > > > > > > No. But if you see illumination value of -1 lumen, do you really > > > > > expect a *lot* of light? > > > > > > > > Not really. I'd rather intrepret it as "the number is not to be trusted", > > > > which is what it means. > > > > > > > > The problem with "all ones" is that it depends on the size of the underlying > > > > data type, which is not nice. Also, if you want that to be a "big number", > > > > there's no clear rule to tell what the number should actually be. > > > > > > > > Anyway, this really is a matter of definition. If we document the attribute > > > > to read as "-1" in specific circumstances, the user space will have to take > > > > that into account. > > > > > > Well, I'd prefer to specify -1 as "underflow" and 1000000000 as > > > "overflow". Any numbers should work, but ... lets make the interface > > > logical if we can. > > > > The interface is already defined, isn't it? And we're now > > considering whether > > No, I don't think it is "already defined". ACPI Specification 4.0, Section 9.2.2, p. 335, defines the interface quite clearly. It actually is defined as "Ones (-1)", but as I said previously, the "all ones" version is not really convenient for sysfs. I don't think the attribute should return anything other than the values defined by the spec, because anyone searching for documentation will first look into the spec. As I said before, I don't think we have any reason _whatsoever_ to translate the spec-defined values to anything else. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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