Re: [Xenomai-help] rt_pipe_stream: not getting EPIPE

[varname <varname@domain.hid>]

Philippe Gerum wrote:
> On Mon, 2011-02-21 at 18:54 +0100, varname wrote:
>> trying to write a simple producer / consumer using message pipes in
>> the native API, this phrase from the documentation (found here [1])
>> confuses me:
>>
>> "-EPIPE is returned if the associated special device is not yet open."
>>
>> It's not so much the sentence itself, but more the fact that I'm not
>> getting that return value from rt_pipe_stream() when streaming bytes
>> to a RT_PIPE that hasn't had its "special device" opened in secondary
>> domain.
>>
>> I've attached a modified trivial-periodic.c that demonstrates what I'm
>> seeing. Afaik there is nothing open(2)-ing the /dev/rtp9 in the
>> secondary domain. All writes succeed, up to about write 31 (*1024),
>> after which all writes return 0.
>>
>> [..]
>> wrote: 1024, res: 1024
>> wrote: 1024, res: 948
>> wrote: 1024, res: 0
>> wrote: 1024, res: 0
>> [..]
>>
>> Is the documentation incorrect, or am I misunderstanding something?
> 
> The doc is wrong (former implementation, 2.1.x series), the pipe
> services do buffer real-time output until the special device is
> eventually opened starting with Xenomai 2.2.x. Since you are using
> rt_pipe_stream(), the output is directed to an internal buffer until
> there is no more space there, which causes the final 0-byte returns.
> 
> So everything looks ok, except the doc.

ok, so there is actually no way to detect whether or not the special 
device has been opened? As I understood from earlier mails on the list, 
writes to a full pipe buffer just fail, correct?

Is there any way to flush a message pipe from a userspace task (as 
opposed to a kernelspace one, where rt_pipe_flush is available)?


thanks for the swift reply