From 32759d402e7327865ea18a203bd1c09f98735bd1 Mon Sep 17 00:00:00 2001 From: Laurent Bercot Date: Sun, 22 Oct 2017 17:09:25 +0000 Subject: Initial commit --- doc/mdevd.html | 130 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 130 insertions(+) create mode 100644 doc/mdevd.html (limited to 'doc/mdevd.html') 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 @@ + + + + + + mdevd: the mdevd program + + + + + + +

+mdevd
+Software
+skarnet.org +

+ +

The `mdevd` program

+ +

+mdevd 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 /dev, etc. +

+ +

+ mdevd's configuration file uses the exact same +format as +mdev. +The differences between mdevd and mdev are: +

+ +

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.
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 +mdevd-netlink, which reads +uevents from the netlink, or with +mdevd-coldplug, which generates +coldplug uevents.

+ +

Interface

+ +

+     mdevd [ -v verbosity ] [ -f conffile ] [ -n ] [ -s slashsys ] [ -d slashdev ] [ -F fwbase ]
+

+ +

mdevd reads and parses its configuration file /etc/mdev.conf.
It then reads its stdin, waiting for uevents. +
It exits when it has finished scanning.

+ +

Exit codes

+ +

0: EOF read on mdevd's stdin
1: received an invalid event
100: wrong usage
111: system call failed

+ +

Signals

+ +

+ mdevd reacts to the following signals: +

+ +

SIGHUP: re-read the configuration file

+ +

Options

+ +

-v verbosity : be more or less verbose. +Default verbosity is 1. 0 will only print fatal error messages, 3 or more +is seriously verbose debugging.
-n : 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.
-f conffile : read the configuration +file from conffile. Default is /etc/mdev.conf.
-s slashsys : assume the sysfs +pseudo-filesystem is mounted on slashsys. Default is /sys.
-d slashdev : assume the device nodes +are to be found in slashdev. Default is /dev.
-F fwbase : assume the firmware files, if any, +are to be found in fwbase. Default is /lib/firmware.

+ +

Configuration file

+ +

+ mdevd uses mdev's configuration file format. +A good mdev.conf example is available +here. +

+ +

+ 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. +

+ +

Notes

+ +

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 +mdevd-coldplug.
However, when paired with mdevd-netlink, +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.

+ + + -- cgit v1.2.3