Re: [Xenomai-help] Re: problem with reading from rt_pipe with a normal linux process

[Philippe Gerum <rpm@xenomai.org>]

On Thu, 2006-08-03 at 09:10 +0200, Marco Jackel wrote:
> Jan Kiszka wrote:
> > Marco Jackel wrote:
> >> Jan Kiszka wrote:
> >>> Hint: read returns its error code in errno. What does that one tell you?
> >> read returns -1, "operation not permitted"
> >>
> > 
> > errno == EPERM? A bit weird. Try strace'ing both your program and the
> > cat tool to look for a difference.
> strace says "-1" in this case is ENOBUFS
> 
> The failure in my programm is that it writes binary data to a pipe with
> rt_pipe_write (preserves message boundary) and normal linux process
> wants to read it byte by byte with read(). Read wants to receive the
> whole message, but the message is bigger than 1 byte, so it returns ENOBUFS.
> 

Yep. Well, I agree that this is clearly not the best designed part of
the entire interface...

> The solution is to use rt_pipe_stream (don't preserves message
> boundary). Do I have to use rt_pipe_alloc before? 

No, rt_pipe_stream() manages an internal buffer to convey the byte
stream, and deals with the rt_pipe_alloc/free interface on its own. You
just need to pass it the raw data buffer and size.

> Is there a small
> sample program somewhere?
> 
> 
> Thanks,
> Marco
> 
> 
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-- 
Philippe.