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<TITLE>Advanced Linux Sound Architecture - Driver: File operations</TITLE>
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<H2><A NAME="s3">3. File operations</A></H2>
<P>File operations related structures and function is in <I>include/driver.h</I>
header file. Basic structure for registering fileoperations for minor number
is <I>snd_minor_t</I>. Minor constants are in <I>include/minors.h</I>
header file.</P>
<H2><A NAME="ss3.1">3.1 Variables and functions</A></H2>
<P>Functions list:</P>
<P>
<UL>
<LI><B>int snd_register_minor( unsigned short minor, snd_minor_t *reg )</B>
<UL>
<LI><B>minor</B> minor number</LI>
<LI><B>reg</B> pointer to registration structure with file operations</LI>
<LI>returns negative value when error occured</LI>
</UL>
</LI>
<LI><B>int snd_unregister_minor( unsigned short minor )</B>
<UL>
<LI><B>minor</B> minor number</LI>
<LI>returns negative value when error occured</LI>
</UL>
</LI>
</UL>
</P>
<P><B>Note:</B> Devices (minor numbers) are registered only if device is
present in the system. It isn't preffered do some pre-registration from
some middle-level code for each possible devices per interface.</P>
<H2><A NAME="ss3.2">3.2 Examples</A></H2>
<P>
<BLOCKQUOTE><CODE>
<HR>
<PRE>
static snd_minor_t snd_pcm_reg = {
"digital audio",
NULL, /* unregister */
NULL, /* lseek */
snd_pcm_read, /* read */
snd_pcm_write, /* write */
snd_pcm_open, /* open */
snd_pcm_release, /* release */
#ifdef SND_POLL
snd_pcm_poll, /* poll */
#else
snd_pcm_select, /* select */
#endif
snd_pcm_ioctl, /* ioctl */
NULL, /* mmap */
};
...
if ( (err = snd_register_minor( SND_MINOR_PCM + device, &snd_pcm_reg )) < 0 )
return err;
...
snd_unregister_minor( SND_MINOR_PCM + device );
</PRE>
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</CODE></BLOCKQUOTE>
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