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No medium Found, 5.0, Notes
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<a href="400-notes.html" >Prev</a>,
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<h1>
5. Strange and Interesting System Calls
</h1>
<ul>
<li> one strerror-equivalent per system call
<li> boundary conditions
<li> multiple causes for the same <i>errno</i> value
<li> multiple <i>errno</i> values for the same cause
<li> coders@slug mailing list
</ul>
<h2> <a name="5.1">5.1</a> ENOMEDIUM </h2>
<ul>
<li> of course, they are all frauds; <a href="500-slide.html" >slide</a>
<li> Native English speakers don't know that “media” is a plural,
let alone that “medium” is its singular.
<li> this <i>strerror</i>(3) string is almost content-free.
<li> surely this could be more informative; <a href="510-slide.html" >slide</a>
<li> O_NONBLOCK
<li> it also groks floppies, magnetic tapes, MMC card readers, <i>etc</i>
<li> disc-with-a-c <i>vs</i> disk-with-a-k
</ul>
<h2> <a name="5.2">5.2</a> EFAULT </h2>
<ul>
<li> one pointer is easy; <a href="520-slide.html" >slide</a>
<li> must not disturb process (thread) signal handlers
<li> bounded memory: <i>mincore</i>(2)
<li> strings: <i>lstat</i>(2)
</ul>
<h2> <a name="5.3">5.3</a> EMFILE </h2>
<ul>
<li> The message includes the limit; <a href="530-slide.html" >slide</a>
<li> can't use <tt>/proc</tt>
<li> <i>sysconf</i>(3) is very handy
<li> of course, it could be a single-open device that
is already open or mounted
</ul>
<h2> <a name="5.4">5.4</a> ENFILE </h2>
<ul>
<li> The message includes the limit; <a href="540-slide.html" >slide</a>
<li> can't use <tt>/proc</tt>
<li> <i>sysconf</i>(3) is very handy
<li> this is when you read kernel sources
<li> system call with no [e]glibc binding<br>
<tt>CTL_FS, FS_MAXFILE</tt>
</ul>
<h2> <a name="5.5">5.5</a> EPERM <i>vs</i> ENOSYS </h2>
<ul>
<li> also EINVAL sometimes
<li> same cause, different <i>errno</i>(3) values;
<a href="550-slide.html" >slide</a>
<li> same <i>errno</i>(3) value, different causes;
<a href="551-slide.html" >slide</a>
<li> wishlist: pathconf for "is this fops pointer non-null"
</ul>
<h2> <a name="5.6">5.6</a> <i>errno</i>(3) is not always set </h2>
<ul>
<li> <a href="560-slide.html" >slide</a>
<li> <i>somtimes</i> they set <i>errno</i>(3),
sometimes they don't.
<li> traps for young players (old ones, too)
<li> not going into each one, read the paper
<li> who knew that <i>fileno</i>(3) could fail?
</ul>
<h2> <a name="5.7">5.7</a> ENOSPC </h2>
<ul>
<li> <a href="570-slide.html" >slide</a>
<li> print the mount point
<li> work in progress (inodes vs data vs directory entries)
<li> special devices already includes device name...
<li> &...need to add device size, without altering state
</ul>
<h2> <a name="5.8">5.8</a> EROFS </h2>
<ul>
<li> file systems print the mount point; <a href="580-slide.html" >slide</a>
<li> devices are more specific
<li> work in progress: filesys case could drill down
<li> work in progress: not all devices this accurate<br/>
\&...because a CD-ROM is not writable<br/>
\&...because the memory card has the write protect tab set<br/>
\&...because the ½ inch magnetic tape does not have a write ring<br/>
</ul>
<h2> <a name="5.9">5.9</a> <i>rename</i>(2) </h2>
<ul>
<li> not talking about <i>mv</i><(1)
<li> <i>rename</i>(2) directory over directory;
<a href="590-slide.html" >slide</a>
<li> destination must be empty
<li> implies all the <i>rmdir</i>(2) errors as well
<li> but not files over directories, or <i>vice versa</i>
<li> who knew: <i>dup2</i>(2) is the same
<li> ...implies all the <i>unlink</i>(2) errors as well
</ul>
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