Re: [Xenomai-help] uClinux write to pipe returning -ENOMEM

[Philippe Gerum <rpm@xenomai.org>]

Filip Van Rillaer wrote:
> Hello,
>  
> I am opening the uClinux side of a Xenomai pipe like (so in blocking mode):
> FdPipe = open(PipeName, O_RDWR);
> After some writes to FdPipe I get the returnvalue -ENOMEM.
> I can understand that the internal buffer gets full as my application is
> writing data faster than the Xenomai side is consuming, but I don't
> expect to see a returnvalue -ENOMEM : the calling writing-thread should
> block, isn't it?  Please comment.
>

RT is assumed to consume asap and will preempt the non-RT write() caller
immediately upon data receipt, unless the RT code uses some kind of timed
polling, which is considered useless and inefficient, since you can ask a RT
thread to wait for incoming data in a blocking way.

> (When adding the O_SYNC flag things get even worse)
>  

That is the point that would actually need fixing: what happens with O_SYNC,
what is worsening exactly?

> Why is the code for xnpipe_write saying:
> if (!mh)
>   /* Cannot sleep. */   <--- ???????????????????
>   return -ENOMEM;
>  
> I am using svn version 4105.
>  
> Best regards,
> Filip
> 
> 
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-- 
Philippe.