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No Medium Found, 6.0, Notes
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<a href="500-notes.html" >Prev</a>,
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<h1>
6. Adventures in <i>ioctl</i>(2) Support
</h1>
<ul>
<li> See <i>ioctl_list</i>(2)
</ul>
<h2> <a name="6.1">6.1</a> Decoding Request Numbers </h2>
<ul>
<li> first impression: large but limited set
<li> switch: they don't play well together<br/>
one ioctl handler per source file
<li> reality: private request numbers
<li> ambiguity: private <i>and</i> historical (look at file descriptor)
<li> internal table of pointers (not a problem yet);
<a href="600-slide.html" >slide</a>
<li> ...each has optional "method" to disambiguate
<li> URL.. follow along the source code
</ul>
<h2> <a name="6.2">6.2</a> Representation </h2>
<ul>
<li> "fildes" is handled the same way as the other system calls
<li> "request" is handled on previous slide
<li> accurate representation of 3rd argument;
<a href="620-slide.html" >slide</a>
<li> ...each ioctl request has "method" to print data
<li> ...output-only requests just print the pointer
</ul>
<h2> <a name="6.3">6.3</a> Explanations </h2>
<ul>
<li> each ioctl request has "method" to print explanation;
<a href="630-slide.html" >slide</a>
<li> set set of <i>errno</i>(3) value usually not documented
<li> this is where you read kernel source
</ul>
<h2> <a name="6.4">6.4</a> EINVAL <i>vs</i> ENOTTY </h2>
<ul>
<li> like system calls, this is messy;
<a href="640-slide.html" >slide</a>
<li> kernel source comments indicate this may be being dealt with
<li> also: ENOSYS, ENOTSUP EOPNOTSUP, and (not Linux) ENOIOCTL
</ul>
<h2> <a name="6.5">6.5</a> intptr_t </h2>
<ul>
<li> shoe-horn
<li> prototype;
<a href="650-slide.html" >slide</a>
<li> ...bye bye type safety
<li> <i>tcflush</i>(3) and friends
<li> [e]glibc internally: two ways
<li> sys_ioctl
<li> cognitive dissonance = bugs
<li> intptr_t
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