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

Greg Kroah-Hartman
2014-09-16T21:33:57Z

On Tue, Sep 16, 2014 at 02:27:15PM -0700, Darren Hart wrote:
> 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@gmail.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.
> >
> > This is probably a good thing to add to sysfs-rules.txt. I'll prepare a patch.
> >
>
> What do people think of appending this to sysfs-rules.txt?
>
> - When reading and writing sysfs device attribute files, avoid dependency
> on specific error codes wherever possible. This minimizes coupling to
> the error handling implemementation within the kernel.
>
> In general, failures to read or write sysfs device attributes shall
> propogate errors wherever possible. Common errors include, but are not
> limited to:
>
> -EIO: The read or store operation is not supported, typically returned by
> the sysfs system itself if the read or store pointer is NULL.
>
> -ENXIO: The read or store operation failed
>
> Error codes will not be changed without good reason, and should a change
> to error codes result in user-space breakage, it will be fixed, or the
> the offending change will be reverted.
>
> Userspace applications can, however, expect the format and contents of
> the attribute files to remain consistent in the absence of a version
> attribute change in the context of a given attributes.

Looks reasonable, thanks. Care to turn it into a patch that I can
apply?

thanks,

greg k-h