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diff --git a/doc/mdevd.html b/doc/mdevd.html new file mode 100644 index 0000000..b5b8a36 --- /dev/null +++ b/doc/mdevd.html @@ -0,0 +1,130 @@ +<html> + <head> + <meta name="viewport" content="width=device-width, initial-scale=1.0" /> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>mdevd: the mdevd program</title> + <meta name="Description" content="mdevd: the mdevd program" /> + <meta name="Keywords" content="mdevd linux administration root utilities devd mdev uevent netlink hotplug manager" /> + <!-- <link rel="stylesheet" type="text/css" href="//skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">mdevd</a><br /> +<a href="//skarnet.org/software/">Software</a><br /> +<a href="//skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>mdevd</tt> program </h1> + +<p> +<tt>mdevd</tt> is an uevent manager. It reads a series of +uevents on its stdin; for every uevent it reads, it performs +actions according to its configuration file. Actions can +be inserting a kernel module, creating or modifying device +entries in <tt>/dev</tt>, etc. +</p> + +<p> + <tt>mdevd</tt>'s configuration file uses the exact same +format as +<a href="https://git.busybox.net/busybox/plain/docs/mdev.txt">mdev</a>. +The differences between mdevd and mdev are: +</p> + +<ul> + <li> mdev needs to be registered as a hotplug manager and the +kernel spawns an instance of mdev per uevent; for every uevent, +mdev has to parse its configuration file. By contrast, there +is only one instance of mdevd, reading a series of uevents and +performing actions without forking; the configuration file is +read and parsed only once. </li> + <li> mdevd reads uevents on its stdin. It is not suitable as +a hotplug manager, and it does not connect to the netlink itself +either. It is meant to be used in conjunction with +<a href="mdevd-netlink.html">mdevd-netlink</a>, which reads +uevents from the netlink, or with +<a href="mdevd-coldplug.html">mdevd-coldplug</a>, which generates +coldplug uevents. </li> +</ul> + +<h2> Interface </h2> + +<pre> + mdevd [ -v <em>verbosity</em> ] [ -f <em>conffile</em> ] [ -n ] [ -s <em>slashsys</em> ] [ -d <em>slashdev</em> ] [ -F <em>fwbase</em> ] +</pre> + +<ul> + <li> mdevd reads and parses its configuration file <tt>/etc/mdev.conf</tt>. </li> + <li> It then reads its stdin, waiting for uevents. + <li> It exits when it has finished scanning. </li> +</ul> + +<h2> Exit codes </h2> + +<ul> + <li> 0: EOF read on mdevd's stdin </li> + <li> 1: received an invalid event </li> + <li> 100: wrong usage </li> + <li> 111: system call failed </li> +</ul> + +<h2> Signals </h2> + +<p> + mdevd reacts to the following signals: +</p> + +<ul> + <li> SIGHUP: re-read the configuration file </li> +</ul> + +<h2> Options </h2> + +<ul> + <li> <tt>-v</tt> <em>verbosity</em> : be more or less verbose. +Default verbosity is 1. 0 will only print fatal error messages, 3 or more +is seriously verbose debugging. </li> + <li> <tt>-n</tt> : dry run. mdevd will not create or delete +device nodes, and it will not spawn commands. Instead, it will print to stdout +the commands it would have spawned. </li> + <li> <tt>-f</tt> <em>conffile</em> : read the configuration +file from <em>conffile</em>. Default is <tt>/etc/mdev.conf</tt>. </li> + <li> <tt>-s</tt> <em>slashsys</em> : assume the sysfs +pseudo-filesystem is mounted on <em>slashsys</em>. Default is <tt>/sys</tt>. </li> + <li> <tt>-d</tt> <em>slashdev</em> : assume the device nodes +are to be found in <em>slashdev</em>. Default is <tt>/dev</tt>. </li> + <li> <tt>-F</tt> <em>fwbase</em> : assume the firmware files, if any, +are to be found in <em>fwbase</em>. Default is <tt>/lib/firmware</tt>. </li> +</ul> + +<h2> Configuration file </h2> + +<p> + mdevd uses mdev's configuration file format. +A good <tt>mdev.conf</tt> example is available +<a href="https://github.com/slashbeast/mdev-like-a-boss/blob/master/mdev.conf">here.</a> +</p> + +<p> + If mdevd cannot find its configuration file, it will use a simple, basic default +configuration where it can create device nodes as root or delete them, and does +nothing else. +</p> + +<h2> Notes </h2> + +<ul> + <li> Strictly speaking, mdevd is a short-lived program: it has +a normal exit condition, which is when it receives EOF on its stdin. +That allows it to work as a coldplug manager when paired with +<a href="mdevd-coldplug.html">mdevd-coldplug</a>. </li> + <li> However, when paired with <a href="mdevd-netlink.html">mdevd-netlink</a>, +it acts as a daemon, because mdev-netlink normally never exits until +the end of the machine lifetime and never closes its stdout, so +mdevd's stdin never receives EOF. </li> +</ul> + +</body> +</html> |