POSIX and return codes...

[Sebastian Huber]

----- Am 27. Feb 2018 um 13:11 schrieb Jakob Viketoft jakob.viketoft at aacmicrotec.com:

> From: Joel Sherrill [joel at rtems.org]
> Sent: Monday, February 26, 2018 14:36
>>> On Feb 26, 2018 8:27 AM, "Jakob Viketoft" <jakob.viketoft at aacmicrotec.com>
>>> wrote:
> 
>>> Hello Joel,
> 
>>> From: Joel Sherrill [joel at rtems.org]
>>> Sent: Monday, February 26, 2018 12:21
> 
>>>> On Feb 26, 2018 5:13 AM, "Jakob Viketoft" <jakob.viketoft at aacmicrotec.com>
>>>> wrote:
>>>>> E.g. could it be possible for the translation mechanism to look if there is
>>>>> already an errno defined and then return this instead of doing the error code
>>>>> translation?
> 
>>>>> It seems like the translation I'm talking about happens in the
>>>>> rtems_deviceio_write() function in cpukit/libcsupport/src/sup_fs_deviceio.c
> 
>>>> Completely random thought as I sit on a plane without code.
> 
>>>> Add a field to the arguments structure for errno. See it to zero before the
>>>> call. If it is set to non-zero after the call, then the driver wanted to return
>>>> errno directly. Otherwise translate.
> 
>>> This was my thought as well, I just wanted to bounce it off the RTEMS list and
>>> also possibly get official support for a feature as this.
> 
>> Now boarded on a different plane and have had another round of thinking.
> 
>> What if an RTEMS status code were added like RTEMS_STATUS_IN_ERRNO and we don't
>> modify the arguments structure. Then a driver could return that status to trip
>> -1 and errno.
> 
> Yes, that would work just as well for us and is even less work / impact.
> 
>> Just a thought. I think it would make the code cleaner but another core
>> developer should pipe up. I was up at 3am to catch a flight and could be loopy.
>> :)
> 
> Anyone else? :)

I think you try to improve the wrong driver framework. This classic device support is a legacy API. It is inflexible and has a considerable overhead due to an excessive layering and the use of minor numbers. A driver registered via IMFS_make_generic_node() already provides the functionality you are asking.