Re: [PATCH v2 3/3] dmi: Make dmi_walk and dmi_walk_early return real error codes

[Andy Lutomirski]

On Tue, Jan 19, 2016 at 1:40 AM, Jean Delvare <jdelvare@xxxxxxx> wrote:
> On Tue, 19 Jan 2016 10:07:36 +0100, Pali RohÃr wrote:
>> On Tuesday 19 January 2016 10:03:03 Jean Delvare wrote:
>> > Hi Pali,
>> >
>> > On Tue, 19 Jan 2016 09:36:33 +0100, Pali RohÃr wrote:
>> > > On Tuesday 19 January 2016 08:54:26 Jean Delvare wrote:
>> > > > > @@ -978,11 +978,11 @@ int dmi_walk(void (*decode)(const struct dmi_header *, void *),
>> > > > >       u8 *buf;
>> > > > >
>> > > > >       if (!dmi_available)
>> > > > > -             return -1;
>> > > > > +             return -ENOENT;
>> > > >
>> > > > -ENOSYS would seem more appropriate?
>> > >
>> > > IIRC -ENOSYS is for non implemented syscalls.
>> >
>> > I can see a lot of -ENOSYS in include/linux/*.h returned by stubs when
>> > a specific subsystem is not included. Not related to syscalls at all.
>> > This is what lead to my suggestion.
>>
>> https://lkml.org/lkml/2014/8/22/492
>
> Thanks for the pointer, I wasn't aware of that.
>
> It really should be documented. No, checkpatch.pl isn't documentation.
>
> Also the commit sadly doesn't say why using ENOSYS in other contexts is
> considered a bad thing. What actual trouble did it cause?

The trouble is that user code likes to assume that, when a syscall
returns -ENOSYS, that syscall isn't implemented.  Letting ENOSYS leak
out to userspace via a syscall that *is* implemented can confused
things.

>
> Are the current presumably incorrect uses of ENOSYS ultimately going to
> be fixed? If not, I see no point in preventing other use cases.

We at least want to prevent it from newly introduced syscalls.

I'll try to clean up the docs.

--Andy