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

[Philippe Gerum <rpm@xenomai.org>]

On Mon, 2011-02-21 at 18:54 +0100, varname wrote:
> All,
> 
> 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.

> 
> Related info:
>   Xenomai: 2.5.5.2
>   Kernel: 2.6.32.26
> 
> [1] http://www.xenomai.org/documentation/trunk/html/api/group__pipe.html#gb4d85ecda7675a75611500070c28b22e
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-- 
Philippe.