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