[PATCH v4 1/2] cobalt: switch hand over status to -EADV for non-RTDM fd

Jan Kiszka jan.kiszka at siemens.com
Fri Aug 30 19:51:55 CEST 2019


On 30.08.19 19:36, Philippe Gerum wrote:
> On 8/30/19 7:13 PM, Philippe Gerum via Xenomai wrote:
>> On 8/30/19 6:58 PM, Jan Kiszka wrote:
>>> On 30.08.19 18:03, Philippe Gerum wrote:
>>>> Having the RTDM core return -EBADF to indicate that it does not manage
>>>> a file descriptor is a problem, as several drivers also raise this
>>>> error to notify userland about an aborted wait due to a connection
>>>> being dismantled (e.g. RTnet). In this case, libcobalt ends up
>>>> forwarding the aborted request to the glibc, which is wrong.
>>>>
>>>> Switch from -EBADF to -EADV to notify userland that RTDM does not
>>>> manage a file descriptor, which cannot conflict with any sensible
>>>> error code the Cobalt core or any RTDM driver may return.
> 
> <snip>
> 
>>>
>>> I'm seeing a few more suspicious occurrences of EBADF in the core:
>>>
>>> kernel/cobalt/posix/io.c:191:   return -EBADF;
>>> kernel/cobalt/posix/io.c:289:                   return -EBADF;
>>> kernel/cobalt/posix/syscall32.c:742:                    return -EBADF;
>>
>> We still want to receive -EBADF on wrong fildes appearing in select()
>> descriptors.
> 
> FWIW, the rationale for this change is that forwarding a request to
> glibc iff the first fd found in a set is a regular one is really fragile
> and actually never worked properly: what if there is a mixed set of
> rtdm/regular fds, with the first one belonging to RTDM?
> 
> So people should make sure to call libcobalt's version of select() if
> they want to monitor RTDM fds, __STD(select()) otherwise. Relying on a
> silent fallback from libcobalt to glibc solely based on fairly weak
> heuristics is not helping anyone in the end.
> 

Indeed. Do we have a good place for documenting this?

Thanks for clarifying - merged to next now.

Jan

-- 
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux



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