Re: [Xenomai-core] [Xenomai-git] Jan Kiszka : RTDM+POSIX: Avoid leaking binding objects on errors

[Jan Kiszka <jan.kiszka@domain.hid>]

Gilles Chanteperdrix wrote:
> Jan Kiszka wrote:
>> Gilles Chanteperdrix wrote:
>>> Jan Kiszka wrote:
>>>> Jan Kiszka wrote:
>>>>> Jan Kiszka wrote:
>>>>>> Gilles Chanteperdrix wrote:
>>>>>>> GIT version control wrote:
>>>>>>>> diff --git a/ksrc/skins/posix/mq.c b/ksrc/skins/posix/mq.c
>>>>>>>> index 11f47c0..a896031 100644
>>>>>>>> --- a/ksrc/skins/posix/mq.c
>>>>>>>> +++ b/ksrc/skins/posix/mq.c
>>>>>>>> @@ -1283,6 +1283,7 @@ int pse51_mq_select_bind(mqd_t fd, struct xnselector *selector,
>>>>>>>>  	return 0;
>>>>>>>>  
>>>>>>>>        unlock_and_error:
>>>>>>>> +	xnfree(binding):
>>>>>>>>  	xnlock_put_irqrestore(&nklock, s);
>>>>>>>>  	return err;
>>>>>>>>  }
>>>>>>> Ok. Will pull. But I really need to fix that.
>>>>>>>
>>>>>> Ack - now that I see it myself.
>>>>>>
>>>>> I fixed this in my branch and added another patch to transform EIDRM
>>>>> into EBADF when selecting a (half-)deleted RTDM device. Please merge.
>>>>>
>>>> Wait! When the sync object behind some file descriptor is deleted but
>>>> the descriptor itself is still existing, we rather have to return that
>>>> fd signaled from select() instead of letting the call fail. I beed to
>>>> look into this again.
>>> It looks to me like a transitory state, we can wait for the sync object
>>> to be deleted to have the fd destructor signaled. It should not be long.
>> That's not an issue of waiting for this. See e.g. TCP: peer closes
>> connection -> internal sync objects will be destroyed (to make
>> read/write fail). But the fd will remain valid until the local side
>> closes it as well.
> 
> It looks to me like this is going to complicate things a lot, and will
> be a source of regressions. Why can we not have sync objects be
> destroyed when the fd is really destroyed and use a status bit of some
> kind to signal read/write that the fd was closed by peer?

It is way easier and more consistent to unblock reader and writers via
destroying the sync object than to signal it and add tests for specific
states to detect that. Keep in mind that this pattern is in use even
without select support. Diverging from it just to add select awareness
to some driver would be a step back.

Jan

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