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<!-- name="Oliver Rauch" -->
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<!-- subject="Re: Backend development problems." -->
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<title>sane-devel: Re: Backend development problems.</title>
<h1>Re: Backend development problems.</h1>
<b>Oliver Rauch</b> (<a href="mailto:oliver.rauch@Wolfsburg.DE"><i>oliver.rauch@Wolfsburg.DE</i></a>)<br>
<i>Mon, 22 Nov 1999 00:03:52 +0100</i>
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<li> <b>Next message:</b> <a href="0203.html">Oliver Rauch: "Re: Please test sane cvs - soname of backend libs"</a>
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<li> <b>Maybe in reply to:</b> <a href="0198.html">Dave Restall - System Administrator: "Backend development problems."</a>
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Dave Restall - System Administrator wrote:<br>
<p>
<i>&gt; Hi,</i><br>
<i>&gt;</i><br>
<i>&gt; I've started and am having a problem :-(</i><br>
<i>&gt;</i><br>
<i>&gt; Why do none of the existing backends follow the standard ? They all do</i><br>
<i>&gt; far more in sane_init than the standard requires.</i><br>
<i>&gt;</i><br>
<p>
They all follow that standrard. It is defined that a frontend has to call<br>
sane_init before it calls any other sane_* function. It also is defined<br>
what has to be done with the parameters version_code and<br>
authoraziation_callback, but it is NOT defined that the backend HAS<br>
TO DO NOTHING ELSE!<br>
<p>
If a backend supports more than one device it has to creat a list of<br>
available devices. This can be done in sane_get_devices and in<br>
sane_open, but it is not forbidden to create this list in sane_init.<br>
<p>
<i>&gt;</i><br>
<i>&gt; I created all the routines as stubs and put the single line in them</i><br>
<i>&gt; saying :-</i><br>
<i>&gt;</i><br>
<i>&gt; printf("In routine ROUTINE_NAME\n");</i><br>
<i>&gt;</i><br>
<i>&gt; and making them return SANE_STATUS_GOOD,</i><br>
<i>&gt;</i><br>
<i>&gt; using scanimage -d pie:/dev/sg2 I would expect the following output :-</i><br>
<i>&gt;</i><br>
<i>&gt; In Routine sane_init</i><br>
<i>&gt; In Routine sane_open</i><br>
<i>&gt;</i><br>
<i>&gt; etc. ala page 32 of the spec.</i><br>
<i>&gt;</i><br>
<i>&gt; I don't get this, all I get is :-</i><br>
<i>&gt;</i><br>
<i>&gt; In Routine sane_init</i><br>
<i>&gt; scanimage: open of device pie:/dev/sg2 failed: Invalid argument</i><br>
<p>
If I do that with the umax backend, I get exact what you expect:<br>
<p>
$ scanimage -d umax:/dev/sga 2&gt;&amp;1 1&gt;/dev/null | grep sane_<br>
[umax] sane_init<br>
[umax] sane_open<br>
...<br>
<p>
Bye<br>
Oliver<br>
<p>
<pre>
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<ul>
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<li> <b>Next message:</b> <a href="0203.html">Oliver Rauch: "Re: Please test sane cvs - soname of backend libs"</a>
<li> <b>Previous message:</b> <a href="0201.html">Oliver Rauch: "Re: Problem with SANE and SCSI scanner"</a>
<li> <b>Maybe in reply to:</b> <a href="0198.html">Dave Restall - System Administrator: "Backend development problems."</a>
<!-- nextthread="start" -->
<li> <b>Next in thread:</b> <a href="0213.html">Dave Restall - System Administrator: "Re:- Re: Backend development problems."</a>
<li> <b>Reply:</b> <a href="0213.html">Dave Restall - System Administrator: "Re:- Re: Backend development problems."</a>
<li> <b>Reply:</b> <a href="0215.html">Randolph Bentson: "Re:- Re: Backend development problems."</a>
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</ul>