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Diffstat (limited to 'doc/s6-devd.html')
| -rw-r--r-- | doc/s6-devd.html | 44 |
1 files changed, 21 insertions, 23 deletions
diff --git a/doc/s6-devd.html b/doc/s6-devd.html index c67429a..60fee03 100644 --- a/doc/s6-devd.html +++ b/doc/s6-devd.html @@ -4,7 +4,7 @@ <meta http-equiv="Content-Language" content="en" /> <title>s6-linux-utils: the s6-devd program</title> <meta name="Description" content="s6-linux-utils: the s6-devd program" /> - <meta name="Keywords" content="s6 linux administration root utilities devd mdev udev" /> + <meta name="Keywords" content="s6 linux administration root utilities devd mdev udev s6-uevent-listener s6-uevent-spawner" /> <!-- <link rel="stylesheet" type="text/css" href="http://skarnet.org/default.css" /> --> </head> <body> @@ -26,20 +26,19 @@ interface does. <h2> Interface </h2> <pre> - s6-devd [ -q | -v ] [ -b kbufsz ] [ -t l:t:k ] <em>prog...</em> + s6-devd [ -q | -v ] [ -b <em>kbufsz</em> ] [ -l <em>linevar</em> ] [ -t l:t:k ] <em>prog...</em> </pre> <ul> - <li> s6-devd binds to the netlink interface and listens for -hotplug events, as the <em>udev</em> program does. </li> - <li> For every event it receives, it spawns <em>prog...</em> with -the event variables added to the environment, just as if <em>prog...</em> -had been registered in <tt>/proc/sys/kernel/hotplug</tt>. </li> - <li> However, unlike the kernel, s6-devd spawns the <em>prog...</em> helpers -sequentially: it waits for an instance to finish before spawning another one. </li> - <li> s6-devd is a long-lived program; it exits 0 when it receives a -SIGTERM. If a helper program is alive at that time, s6-devd waits for it to die -before exiting. </li> + <li> s6-devd rewrites its command line into +<tt><a href="s6-uevent-listener.html">s6-uevent-listener</a> +<a href="s6-uevent-spawner.html">s6-uevent-spawner</a> <em>prog...</em></tt>, +dispatching its options to the appropriate program; then it execs into +this command line. </li> + <li> The <a href="s6-uevent-listener.html">s6-uevent-listener</a> +will listen to the netlink and pass the events sequentially to +<a href="s6-uevent-spawner.html">s6-uevent-spawner</a>, which will +spawn a <em>prog...</em> helper for every event. </li> </ul> <h2> Options </h2> @@ -47,9 +46,13 @@ before exiting. </li> <ul> <li> <tt>-q</tt> : be more quiet. </li> <li> <tt>-v</tt> : be more verbose. </li> - <li> <tt>-b</tt> <em>kbufsz</em> : try and reserve a kernel buffer of + <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. </li> + <li> <tt>-l</tt> <em>linevar</em> : the short description of the +event, given by the kernel as the first string in the netlink message, +will be made available to <em>prog</em> under the environment variable +named <em>linevar</em>. </li> <li> <tt>-t</tt> <em>l:t:k</em> : If <em>l</em>, <em>t</em> or <em>k</em> is specified, they specify timeouts; by default, they are infinite. If <em>prog...</em> is still alive after <em>l</em> milliseconds, s6-devd sends @@ -62,18 +65,13 @@ alive after <em>k</em> more milliseconds, s6-devd yells and exits 99. </li> <ul> <li> s6-devd is a daemon; it should be run under a proper supervision system such -as <a href="http://skarnet.org/software/s6/">s6</a>. (That is why it does not -fork and logs to stderr.) </li> +as <a href="http://skarnet.org/software/s6/">s6</a>. The real long-lived +process is named <a href="s6-uevent-listener.html">s6-uevent-listener</a>; +ir runs with the same pid as s6-devd. </li> <li> The <em>prog...</em> helper, on the other hand, should be very short-lived, even if you are not using the <tt>-t</tt> option to s6-devd. Since helpers are -spawned sequentially, slow helpers can make events queue up and fill the netlink -kernel buffer. </li> - <li> If you are using <a href="http://busybox.net/">busybox</a> and want a -minimal udev-style dynamic <tt>/dev</tt> -handling, <tt>/sbin/mdev</tt> is a suitable <em>prog...</em> helper. </li> - <li> The point of s6-devd is that it runs the helpers sequentially, so it solves -the race condition that appears when helpers are run via the hotplug interface. -When s6-devd is used, <tt>/proc/sys/kernel/hotplug</tt> should be empty. </li> +spawned sequentially, slow helpers can make events queue up and fill buffers +along the way. </li> </ul> </body> |