From 54b6467013bfbdb3ee606961c02fbff1271ca582 Mon Sep 17 00:00:00 2001 From: Laurent Bercot Date: Fri, 19 Sep 2014 15:01:58 +0000 Subject: initial commit --- doc/s6-devd.html | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 80 insertions(+) create mode 100644 doc/s6-devd.html (limited to 'doc/s6-devd.html') diff --git a/doc/s6-devd.html b/doc/s6-devd.html new file mode 100644 index 0000000..5ae6160 --- /dev/null +++ b/doc/s6-devd.html @@ -0,0 +1,80 @@ + + + + + s6-linux-utils: the s6-devd program + + + + + + +

+s6-linux-utils
+Software
+skarnet.org +

+ +

The `s6-devd` program

+ +

+s6-devd listens to the netlink interface for udev events, and +launches a helper program for every event, similarly to what the hotplug +interface does. +

+ +

Interface

+ +

+     s6-devd [ -q | -v ] [ -b kbufsz ] [ -t l:t:k ] prog...
+

+ +

s6-devd binds to the netlink interface and listens for +hotplug events, as the udev program does.
For every event it receives, it spawns prog... with +the event variables added to the environment, just as if prog... +had been registered in /proc/sys/kernel/hotplug.
However, unlike the kernel, s6-devd spawns the prog... helpers +sequentially: it waits for an instance to finish before spawning another one.�
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.

+ +

Options

+ +

-q : be more quiet.
-v : be more verbose.
-b kbufsz : try and reserve a kernel buffer of +kbufsz bytes for the netlink queue. Too large a buffer wastes kernel memory; +too small a buffer risks losing events. The default is 65536.
-t l:t:k : If l, t or k is +specified, they specify timeouts; by default, they are infinite. +If prog... is still alive after l milliseconds, s6-devd sends +it a SIGTERM. Then, if prog... is still alive after t more +milliseconds, s6-devd sends it a SIGKILL. Then, if prog... is still +alive after k more milliseconds, s6-devd yells and exits 99.

+ +

Notes

+ +

s6-devd is a daemon; it should be run under a proper supervision system such +as s6. (That is why it does not +fork and logs to stderr.)
The prog... helper, on the other hand, should be very short-lived, +even if you are not using the -t option to s6-devd. Since helpers are +spawned sequentially, slow helpers can make events queue up and fill the netlink +kernel buffer.
�If you are using busybox and want a +minimal udev-style dynamic /dev +handling, /sbin/mdev is a suitable prog... helper.
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, /proc/sys/kernel/hotplug should be empty.

+ + + -- cgit v1.2.3

The s6-devd program

Interface

Options

Notes

The `s6-devd` program