From f0f727fbb8576afc7ea31f2b6aacccdd565472d0 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 11 Dec 2013 18:38:51 +0100
Subject: [PATCH] man: explain in more detail how SYSTEMD_READY= influences
SYSTEMD_WANTS= in udev rules
https://bugzilla.redhat.com/show_bug.cgi?id=1026860
---
man/systemd.device.xml | 45 +++++++++++++++++++++++++++++++--------------
1 file changed, 31 insertions(+), 14 deletions(-)
diff --git a/man/systemd.device.xml b/man/systemd.device.xml
index 96ebe89..002b647 100644
--- a/man/systemd.device.xml
+++ b/man/systemd.device.xml
@@ -70,12 +70,15 @@
since no device-specific options may be
configured.</para>
- <para>systemd will automatically create dynamic device
- units for all kernel devices that are marked with the
- "systemd" udev tag (by default all block and network
- devices, and a few others). This may be used to define
- dependencies between devices and other
- units.</para>
+ <para>systemd will dynamically create device units for
+ all kernel devices that are marked with the "systemd"
+ udev tag (by default all block and network devices,
+ and a few others). This may be used to define
+ dependencies between devices and other units. To tag a
+ udev device use <literal>TAG+="systemd"</literal> in
+ the udev rules file, see
+ <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>
+ for details.</para>
<para>Device units are named after the
<filename>/sys</filename> and
@@ -93,7 +96,7 @@
<para>The settings of device units may either be
configured via unit files, or directly from the udev
- database (which is recommended). The following udev
+ database (which is recommended). The following udev device
properties are understood by systemd:</para>
<variablelist class='udev-directives'>
@@ -101,16 +104,26 @@
<term><varname>SYSTEMD_WANTS=</varname></term>
<listitem><para>Adds dependencies of
type <varname>Wants</varname> from
- this unit to all listed units. This
+ the device unit to all listed units. This
may be used to activate arbitrary
- units, when a specific device becomes
+ units when a specific device becomes
available. Note that this and the
other tags are not taken into account
unless the device is tagged with the
<literal>systemd</literal> string in
the udev database, because otherwise
the device is not exposed as systemd
- unit.</para></listitem>
+ unit (see above). Note that systemd
+ will only act on
+ <varname>Wants</varname> dependencies
+ when a device first becomes active, it
+ will not act on them if they are added
+ to devices that are already
+ active. Use
+ <varname>SYSTEMD_READY=</varname> (see
+ below) to influence on which udev
+ event to trigger the device
+ dependencies.</para></listitem>
</varlistentry>
<varlistentry>
@@ -135,10 +148,14 @@
device disappears from the udev
tree. This option is useful to support
devices that initially show up in an
- uninitialized state in the tree, and for
- which a changed event is generated the
- moment they are fully set
- up.</para></listitem>
+ uninitialized state in the tree, and
+ for which a <literal>changed</literal>
+ event is generated the moment they are
+ fully set up. Note that
+ <varname>SYSTEMD_WANTS=</varname> (see
+ above) is not acted on as long as
+ <varname>SYSTEMD_READY=0</varname> is
+ set for a device.</para></listitem>
</varlistentry>
<varlistentry>