open_mode

[Joel Sherrill]

Pattara Kiatisevi wrote:
> 
> Hi,
> 
> I'm working further on my sound driver in the sound_open() function.
> >From application code I do:
> 
> audio_fd = open("/dev/dsp", 4, 1)

I think it was bogus to pass a 4 as the flags arg to open.
You should use the constants O_RDONLY, O_WRONLY, O_RDWR per
POSIX and ISO C. In this particular case, a 4 does not appear
to map to anything.  From sys/fcntl.h

#define O_RDONLY        0               /* +1 == FREAD */
#define O_WRONLY        1               /* +1 == FWRITE */
#define O_RDWR          2               /* +1 == FREAD|FWRITE */         

Also passing the 3rd parameter is bogus because you are not
creating the file /dev/dsp.  Even if you did, using a 1 is
also not cool and you should use the appropriate S_ constants.



> And then in the driver code:
> 
> rtems_device_driver sound_open(
>   rtems_device_major_number major,
>   rtems_device_minor_number minor,
>   void                    * arg
> )
> {
>   rtems_libio_open_close_args_t *args = arg;
> 
>   /* Only write-only mode is supported now */
>   printf("args->flags is 0x%4X\n", args->flags);
>   printf("args->mode is 0x%4X\n", args->mode);
>   if ( args->flags == 0x0004 ) {
>     printf("/dev/dsp opened...\n");
>     return RTEMS_SUCCESSFUL;
>   } else {
>     return RTEMS_NOT_IMPLEMENTED;
>   }
> 
> Hmm, but amazing (to me) is that the debugged output said:
> 
> args->flags is 0x 103
> args->mode is 0x   1
> /dev/dsp: Permission denied
> 
> Hmm, the flag I sent was "4" or "0x0004" but how could it become 0x103?
> Anybody has idea?

It is a bad idea to use numeric constants.  POSIX defined symbols for
a reason. :)

> Thank you,
> Pattara}
> 
> The best things in life are free. - B.G. DeSilva (1927)
> ----------------------------------------------------------------------
> Ott Pattara Kiatisevi                              T L W G
> M.Sc. INFOTECH Student, Stuttgart, Germany      http://linux.thai.net/
> ----------------------------------------------------------------------

-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
   Support Available             (256) 722-9985