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diff --git a/doc/mdevd-netlink.html b/doc/mdevd-netlink.html new file mode 100644 index 0000000..9747f13 --- /dev/null +++ b/doc/mdevd-netlink.html @@ -0,0 +1,123 @@ +<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-netlink program</title> + <meta name="Description" content="mdevd: the mdevd-netlink program" /> + <meta name="Keywords" content="mdevd linux administration root utilities devd mdev udev s6-uevent-listener uevent netlink" /> + <!-- <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-netlink</tt> program </h1> + +<p> +<tt>mdevd-netlink</tt> listens to the netlink interface for uevents +(also called "hotplug" or "udev" events), and writes those uevents to +its standard output, using a simple format. +</p> + +<p> +<a href="mdevd.html">mdevd</a> expects uevents in the same +format mdevd-netlink writes them. So the +<tt>mdevd-netlink | mdevd</tt> command line will function as +a daemon reading uevents from the netlink and handling them. +</p> + +<h2> Interface </h2> + +<pre> + mdevd-netlink [ -d notif ] [ -v <em>verbosity</em> ] [ -b kbufsz ] +</pre> + +<ul> + <li> mdevd-netlink binds to the netlink interface and listens for +hotplug events, as the <em>udevd</em> program does. </li> + <li> It writes event information to its stdout. The output contains +null characters, so a terminal will not display them correctly. To +properly use mdevd-netlink, it should be piped into a handler +program such as <a href="mdevd.html">mdevd</a>. </li> + <li> mdevd-netlink is a long-lived program. +When it receives a SIGTERM, it stops listening to hotplug events; +it will exit as soon as it has flushed its event queue to stdout. </li> +</ul> + +<h2> Options </h2> + +<ul> + <li> <tt>-d</tt> <em>notif</em> : when ready (actually +listening to the netlink), write a newline to file descriptor <em>notif</em> +then close it. This allows mdevd-netlink to use the +<a href="//skarnet.org/software/s6/notifywhenup.html">s6 mechanism to +notify readiness</a>. <em>notif</em> cannot be lesser than 3. If this +option is not given, no readiness notification is sent. </li> + <li> <tt>-v</tt> <em>verbosity</em> : be more or less verbose. +Default verbosity is 1. 0 will only print fatal error messages, 3 will +print warnings every time the netlink interface sends something +unexpected. </li> + <li> <tt>-b</tt> <em>kbufsz</em> : try and reserve a kernel buffer of +<em>kbufsz</em> bytes for the netlink queue. Too large a buffer wastes kernel memory; +too small a buffer risks losing events. The default is 65536 (which is on +the large side). </li> +</ul> + +<h2> Protocol </h2> + +<ul> + <li> An event is a series of null-terminated strings as they are sent by +the kernel to the netlink; mdevd-netlink adds a final empty string +(i.e. an additional null character) to mark the end of the series. </li> + <li> The first string is a short description of the event; it normally +contains the string "@/". Other strings after the first are of the form +"VARIABLE=value", and describe the environment which a hotplug helper +for the event (registered in <tt>/proc/sys/kernel/hotplug</tt>) would be +spawned with. </li> + <li> Example (newlines added for clarity): <pre> +add@/class/input/input9/mouse2\0 +ACTION=add\0 +DEVPATH=/class/input/input9/mouse2\0 +SUBSYSTEM=input\0 +SEQNUM=106\0 +PHYSDEVPATH=/devices/pci0000:00/0000:00:1d.1/usb2/22/22:1.0 +PHYSDEVBUS=usb\0 +PHYSDEVDRIVER=usbhid\0 +MAJOR=13\0 +MINOR=34\0 +\0 </pre> </li> +</ul> + +<h2> Notes </h2> + +<ul> + <li> mdevd-netlink is a daemon; it should be run under a proper supervision system such +as <a href="//skarnet.org/software/s6/">s6</a>. </li> +<li> If you are running mdevd-netlink, the program you pipe its +output into should be the only program handling uevents; that means +that <tt>/proc/sys/kernel/hotplug</tt> should be empty. </li> +<li> The <tt>mdevd-netlink | mdevd</tt> command line is a quick +way of running a uevent manager, but there are ways to improve it: + <ul> + <li> Using the +<a href="//skarnet.org/software/execline/">execline</a> scripting +language, the <tt>pipeline { mdevd-netlink } mdevd</tt> command +line will avoid leaving a shell around. </li> + <li> The best way to use mdevd-netlink and mdevd is with a +supervision system: +under <a href="//skarnet.org/software/s6/">s6</a> or +<a href="//skarnet.org/software/s6-rc/">s6-rc</a>, write a service +pipeline where <tt>mdevd-netlink</tt> is a producer and +<tt>mdevd</tt> is a consumer. This setup has the advantage, among +others, that you can restart the netlink listener and the event handler +separately. </li> + </ul> </li> +</ul> + +</body> +</html> |