linux-kernel - Re: [PATCH 10/13] eeepc-laptop: compare proper return values in get

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Message-ID: <20140916211001.GA23674@gmail.com>
Date:	Tue, 16 Sep 2014 23:10:01 +0200
From:	Frans Klaver <fransklaver@...il.com>
To:	Darren Hart <dvhart@...radead.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Corentin Chary <corentin.chary@...il.com>,
	Rafael Wysocki <rafael.j.wysocki@...el.com>,
	acpi4asus-user <acpi4asus-user@...ts.sourceforge.net>,
	platform-driver-x86 <platform-driver-x86@...r.kernel.org>,
	linux-kernel@...r.kernel.org,
	linux-acpi <linux-acpi@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH 10/13] eeepc-laptop: compare proper return values in
 get_cpufv

On Tue, Sep 16, 2014 at 01:52:47PM -0700, Darren Hart wrote:
> On Tue, Sep 16, 2014 at 01:54:25PM +0200, Frans Klaver wrote:
> > On Mon, Sep 15, 2014 at 11:55 PM, Frans Klaver <fransklaver@...il.com> wrote:
> > > On Mon, Sep 15, 2014 at 02:51:25PM -0700, Greg Kroah-Hartman wrote:
> > >> On Mon, Sep 15, 2014 at 02:49:02PM -0700, Darren Hart wrote:
> > >> >
> > >> > This patch is fine as is. However, Greg has supported propogating the error code
> > >> > through to the sysfs interface (if I understand him correctly on an earlier post
> > >> > to this list). This would require an addition change to this patch would
> > >> > propogated the get_cpufv error code in show_available_cpuv(), show_cpuv(), and
> > >> > store_cpuv(). As it is, we return -ENODEV on any failure, where an ACPI call
> > >> > error should probably return -ENXIO as I understand it.
> > >>
> > >> I really have no idea at this point in time what to recommend.  How
> > >> about just stick with what is happening today so that:
> > >>
> > >> > However, there was a rather famous change in error code handling in which pulse
> > >> > audio broke and Linus was very upset with one of his maintainers.
> > >>
> > >> That doesn't happen :)
> > >
> > > So if I interpret that correctly, we're dropping the last patch
> > > (ENODEV -> ENXIO) from the series? That's fine by me. As mentioned
> > > earlier, I already saw something else break because I returned ENXIO
> > > instead of ENODEV.
> > >
> > > Maybe it's a good idea to try and document the expected behavior
> > > somewhere, if even Greg isn't sure what to do.
> > 
> > For good measure:
> > 
> > v2 will not change the return values at the sysfs interface, meaning
> > we will always return -ENODEV on error. I am going to try to keep as
> > much internal functions propagating errors as possible though, unless
> > someone strongly disagrees.
> > 
> > Thanks,
> > Frans
> 
> I cornered Linus today and asked about this specifically. The policy is this:
> 
> Don't change the sysfs return codes without good reason. A good reason could be
> a real bug or problem with the return codes. It could also be to consolidate
> error handling which makes things more uniform, etc.
> 
> If this results in broken userspace, the maintainer will revert the change.

Alright, that is basically what I was expecting it to be. As it happens,
this also means that we'll have to decide what to do about returning
-EIO/-ENODEV/rv in show_sys_acpi and store_sys_acpi. The latter was
changed by Paul Bolle's "eeepc-laptop: simplify parse_arg()". The return
value of these functions is propagated to the sysfs interface.


> This is probably a good thing to add to sysfs-rules.txt. I'll prepare a patch.

Agreed.

While I was removing the patches changing the sysfs error behavior, I
also noticed that eeepc-laptop.c doesn't really seem to handle errors
uniformly. In some cases the callers of get_acpi and set_acpi don't even
seem to consider that these functions may return an error code (e.g.
eeepc_hotk_thaw()). I'd fix those in a new series though.

Frans
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