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

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

[Marco Jackel]

Hi,
i do the following:

- create a pipe:

rt_pipe_create (&data_pipe, "data_pipe", PIPE_MINOR, PIPE_SIZE);

- write data to the pipe:

rt_pipe_write(&data_pipe, &pipe_buf, pipe_buf_sz, P_NORMAL);

- open the pipe from a normal linux process:

pipe_fd = open(DATA_PIPE, O_RDONLY);

- read the data from the pipe:

ret = read(pipe_fd, &pipe_buf, sizeof(pipe_buf));


Opening works, but the reading doesn't work. I get the error code "-1",
Operation not permitted.

Permission for the device file is ok:

voyage:~# ls -l /dev/rtp0
crw-rw-rw-  1 root root 150, 0 Jun 21  2006 /dev/rtp0


What am I doing wrong?

Thanks
Marco


Linux voyage 2.6.16.1-03-xenomai-2.1.2 #1 PREEMPT Tue Jul 11 10:17:15
GMT 2006 i586 GNU/Linux

Gnu C                  17:
util-linux             2.12p
mount                  2.12p
module-init-tools      3.2-pre1
e2fsprogs              1.37
pcmcia-cs              3.2.5
PPP                    2.4.3
Linux C Library        2.3.2
Dynamic linker (ldd)   2.3.2
Procps                 3.2.1
Net-tools              1.60
Kbd                    69:
Sh-utils               5.2.1
Modules Loaded         xeno_16550A xeno_rtdm uhci_hcd ohci_hcd usbcore
dm_mod

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

[Marco Jackel]

Mhmm, strange, I can read the data with a "cat /dev/rtp0"....


Marco Jackel wrote:
> Hi,
> i do the following:
> 
> - create a pipe:
> 
> rt_pipe_create (&data_pipe, "data_pipe", PIPE_MINOR, PIPE_SIZE);
> 
> - write data to the pipe:
> 
> rt_pipe_write(&data_pipe, &pipe_buf, pipe_buf_sz, P_NORMAL);
> 
> - open the pipe from a normal linux process:
> 
> pipe_fd = open(DATA_PIPE, O_RDONLY);
> 
> - read the data from the pipe:
> 
> ret = read(pipe_fd, &pipe_buf, sizeof(pipe_buf));
> 
> 
> Opening works, but the reading doesn't work. I get the error code "-1",
> Operation not permitted.
> 
> Permission for the device file is ok:
> 
> voyage:~# ls -l /dev/rtp0
> crw-rw-rw-  1 root root 150, 0 Jun 21  2006 /dev/rtp0
> 
> 
> What am I doing wrong?
> 
> Thanks
> Marco
> 
> 
> Linux voyage 2.6.16.1-03-xenomai-2.1.2 #1 PREEMPT Tue Jul 11 10:17:15
> GMT 2006 i586 GNU/Linux
> 
> Gnu C                  17:
> util-linux             2.12p
> mount                  2.12p
> module-init-tools      3.2-pre1
> e2fsprogs              1.37
> pcmcia-cs              3.2.5
> PPP                    2.4.3
> Linux C Library        2.3.2
> Dynamic linker (ldd)   2.3.2
> Procps                 3.2.1
> Net-tools              1.60
> Kbd                    69:
> Sh-utils               5.2.1
> Modules Loaded         xeno_16550A xeno_rtdm uhci_hcd ohci_hcd usbcore
> dm_mod

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

[Jan Kiszka]

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Marco Jackel wrote:
> Mhmm, strange, I can read the data with a "cat /dev/rtp0"....
> 

Hint: read returns its error code in errno. What does that one tell you?

Jan

> 
> Marco Jackel wrote:
>> Hi,
>> i do the following:
>>
>> - create a pipe:
>>
>> rt_pipe_create (&data_pipe, "data_pipe", PIPE_MINOR, PIPE_SIZE);
>>
>> - write data to the pipe:
>>
>> rt_pipe_write(&data_pipe, &pipe_buf, pipe_buf_sz, P_NORMAL);
>>
>> - open the pipe from a normal linux process:
>>
>> pipe_fd = open(DATA_PIPE, O_RDONLY);
>>
>> - read the data from the pipe:
>>
>> ret = read(pipe_fd, &pipe_buf, sizeof(pipe_buf));
>>
>>
>> Opening works, but the reading doesn't work. I get the error code "-1",
>> Operation not permitted.
>>
>> Permission for the device file is ok:
>>
>> voyage:~# ls -l /dev/rtp0
>> crw-rw-rw-  1 root root 150, 0 Jun 21  2006 /dev/rtp0
>>
>>
>> What am I doing wrong?
>>
>> Thanks
>> Marco
>>
>>
>> Linux voyage 2.6.16.1-03-xenomai-2.1.2 #1 PREEMPT Tue Jul 11 10:17:15
>> GMT 2006 i586 GNU/Linux
>>
>> Gnu C                  17:
>> util-linux             2.12p
>> mount                  2.12p
>> module-init-tools      3.2-pre1
>> e2fsprogs              1.37
>> pcmcia-cs              3.2.5
>> PPP                    2.4.3
>> Linux C Library        2.3.2
>> Dynamic linker (ldd)   2.3.2
>> Procps                 3.2.1
>> Net-tools              1.60
>> Kbd                    69:
>> Sh-utils               5.2.1
>> Modules Loaded         xeno_16550A xeno_rtdm uhci_hcd ohci_hcd usbcore
>> dm_mod
> 
> 
> _______________________________________________
> Xenomai-help mailing list
> Xenomai-help@domain.hid
> https://mail.gna.org/listinfo/xenomai-help



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

[Marco Jackel]

Jan Kiszka wrote:
> Hint: read returns its error code in errno. What does that one tell you?

read returns -1, "operation not permitted"

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

[Jan Kiszka]

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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.

Jan


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

[Marco Jackel]

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.

The solution is to use rt_pipe_stream (don't preserves message
boundary). Do I have to use rt_pipe_alloc before? Is there a small
sample program somewhere?


Thanks,
Marco

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

[Philippe Gerum]

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
> 
> 
> _______________________________________________
> Xenomai-help mailing list
> Xenomai-help@domain.hid
> https://mail.gna.org/listinfo/xenomai-help
-- 
Philippe.