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From af528dcffaab1efea760395cc6676fe4b01e89b5 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
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Date: Thu, 9 May 2019 12:34:30 +0200
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Subject: [PATCH] man: describe naming schemes in a new man page
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I decided to make this a separate man page because it is freakin' long.
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This content could equally well go in systemd-udevd.service(8), systemd.link(5),
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or a new man page for the net_id builtin.
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v2:
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- rename to systemd.net-naming-scheme
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- add udevadm test-builtin net_id example
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(cherry picked from commit 0b1e5b6ed8c6b9a2bc53709eb75e381d360f05bf)
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Related: #1827462
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[msekleta: I've removed parts that describe features which are not
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available in RHEL-8]
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---
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 man/rules/meson.build             |   1 +
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 man/systemd-udevd.service.xml     |  19 +-
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 man/systemd.link.xml              |  10 +-
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 man/systemd.net-naming-scheme.xml | 385 ++++++++++++++++++++++++++++++
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 src/udev/udev-builtin-net_id.c    |   1 +
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 5 files changed, 402 insertions(+), 14 deletions(-)
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 create mode 100644 man/systemd.net-naming-scheme.xml
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diff --git a/man/rules/meson.build b/man/rules/meson.build
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index 7ae94ea265..e6c0a99bbd 100644
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--- a/man/rules/meson.build
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+++ b/man/rules/meson.build
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@@ -714,6 +714,7 @@ manpages = [
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  ['systemd.kill', '5', [], ''],
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  ['systemd.link', '5', [], ''],
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  ['systemd.mount', '5', [], ''],
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+ ['systemd.net-naming-scheme', '7', [], ''],
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  ['systemd.netdev', '5', [], 'ENABLE_NETWORKD'],
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  ['systemd.network', '5', [], 'ENABLE_NETWORKD'],
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  ['systemd.nspawn', '5', [], ''],
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diff --git a/man/systemd-udevd.service.xml b/man/systemd-udevd.service.xml
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index b738591c93..f4cdb2f1e7 100644
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--- a/man/systemd-udevd.service.xml
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+++ b/man/systemd-udevd.service.xml
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@@ -174,15 +174,11 @@
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         <term><varname>net.naming-scheme=</varname></term>
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         <listitem>
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           <para>Network interfaces are renamed to give them predictable names when possible (unless
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-          <varname>net.ifnames=0</varname> is specified, see above). The names are derived from various
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-          device metadata fields. Newer versions of <filename>systemd-udevd.service</filename> take more of
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-          these fields into account, improving (and thus possibly changing) the names used for the same
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-          devices. With this kernel command line option it is possible to pick a specific version of this
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-          algorithm. It expects a naming scheme identifier as argument. Currently the following identifiers
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-          are known: <literal>rhel-8.0</literal>, <literal>rhel-8.1</literal>, <literal>rhel-8.2</literal>,
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-          <literal>rhel-8.3</literal> which each implement the naming scheme that was the default in the
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-          indicated Red Hat Enterprise Linux minor version. In addition, <literal>latest</literal> may be
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-          used to designate the latest scheme known (to this particular version of
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+          <varname>net.ifnames=0</varname> is specified, see above). With this kernel command line option it
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+          is possible to pick a specific version of this algorithm and override the default chosen at
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+          compilation time. Expects one of the naming scheme identifiers listed in
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+          <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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+          or <literal>latest</literal> to select the latest scheme known (to this particular version of
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           <filename>systemd-udevd.service</filename>).</para>
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           <para>Note that selecting a specific scheme is not sufficient to fully stabilize interface naming:
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           the naming is generally derived from driver attributes exposed by the kernel. As the kernel is
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@@ -191,9 +187,8 @@
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         </listitem>
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       </varlistentry>
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     </variablelist>
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-    
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-         in kernel-command-line.xml -->
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- </refsect1>
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+    
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+  </refsect1>
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   <refsect1>
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     <title>See Also</title>
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diff --git a/man/systemd.link.xml b/man/systemd.link.xml
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index 6708753e82..32657308d0 100644
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--- a/man/systemd.link.xml
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+++ b/man/systemd.link.xml
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@@ -286,6 +286,7 @@
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                 <para>The name is set based on information given by
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                 the firmware for on-board devices, as exported by the
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                 udev property <literal>ID_NET_NAME_ONBOARD</literal>.
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+                See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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                 </para>
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               </listitem>
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             </varlistentry>
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@@ -295,6 +296,7 @@
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                 <para>The name is set based on information given by
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                 the firmware for hot-plug devices, as exported by the
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                 udev property <literal>ID_NET_NAME_SLOT</literal>.
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+                See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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                 </para>
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               </listitem>
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             </varlistentry>
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@@ -303,7 +305,9 @@
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               <listitem>
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                 <para>The name is set based on the device's physical
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                 location, as exported by the udev property
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-                <literal>ID_NET_NAME_PATH</literal>.</para>
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+                <literal>ID_NET_NAME_PATH</literal>.
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+                See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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+                </para>
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               </listitem>
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             </varlistentry>
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             <varlistentry>
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@@ -311,7 +315,9 @@
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               <listitem>
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                 <para>The name is set based on the device's persistent
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                 MAC address, as exported by the udev property
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-                <literal>ID_NET_NAME_MAC</literal>.</para>
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+                <literal>ID_NET_NAME_MAC</literal>.
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+                See <citerefentry><refentrytitle>systemd.net-naming-scheme</refentrytitle><manvolnum>7</manvolnum></citerefentry>.
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+                </para>
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               </listitem>
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             </varlistentry>
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           </variablelist>
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diff --git a/man/systemd.net-naming-scheme.xml b/man/systemd.net-naming-scheme.xml
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new file mode 100644
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index 0000000000..a12cc3c460
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--- /dev/null
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+++ b/man/systemd.net-naming-scheme.xml
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@@ -0,0 +1,385 @@
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+
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+
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+  "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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+
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+
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+<refentry id="systemd.net-naming-scheme">
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+  <refentryinfo>
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+    <title>systemd.net-naming-scheme</title>
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+    <productname>systemd</productname>
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+  </refentryinfo>
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+
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+  <refmeta>
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+    <refentrytitle>systemd.net-naming-scheme</refentrytitle>
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+    <manvolnum>7</manvolnum>
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+  </refmeta>
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+
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+  <refnamediv>
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+    <refname>systemd.net-naming-scheme</refname>
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+    <refpurpose>Network device naming schemes</refpurpose>
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+  </refnamediv>
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+
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+  <refsect1>
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+    <title>Description</title>
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+
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+    <para>Network interfaces may be renamed to give them predictable names when there's enough information to
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+    generate appropriate names and the use of certain types of names is configured. This page describes the
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+    first part, i.e. what possible names may be generated. Those names are generated by the
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+    <citerefentry><refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>
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+    builtin <command>net_id</command> and exported as udev properties
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+    (<varname>ID_NET_NAME_ONBOARD=</varname>, <varname>ID_NET_LABEL_ONBOARD=</varname>,
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+    <varname>ID_NET_NAME_PATH=</varname>, <varname>ID_NET_NAME_SLOT=</varname>).</para>
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+
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+    <para>Names are derived from various device metadata attributes. Newer versions of udev take more of
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+    these attributes into account, improving (and thus possibly changing) the names used for the same
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+    devices. Differents version of the naming rules are called "naming schemes". The default naming scheme is
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+    chosen at compilation time. Usually this will be the latest implemented version, but it is also possible
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+    to set one of the older versions to preserve compatibility. This may be useful for example for
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+    distributions, which may introduce new versions of systemd in stable releases without changing the naming
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+    scheme. The naming scheme may also be overriden using the <varname>net.naming-scheme=</varname> kernel
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+    command line switch, see
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+    <citerefentry><refentrytitle>systemd-udevd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
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+    Available naming schemes are described below.</para>
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+
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+    <para>After the udev proprties have been generated, appropriate udev rules may be used to actually rename
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+    devices based on those properties. See the description of <varname>NamePolicy=</varname> in
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+    <citerefentry><refentrytitle>systemd.link</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
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+    </para>
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+  </refsect1>
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+
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+  <refsect1>
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+    <title>Naming</title>
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+
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+    <para>All names start with a two-character prefix that signifies the interface type.</para>
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+
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+    
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+      <title>Two character prefixes based on the type of interface</title>
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+
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+      <tgroup cols='2'>
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+        
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+          <row>
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+            <entry>Prefix</entry>
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+            <entry>Description</entry>
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+          </row>
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+        
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+        
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+          <row>
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+            <entry><constant>en</constant></entry>
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+            <entry>Ethernet</entry>
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+          </row>
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+          <row>
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+            <entry><constant>sl</constant></entry>
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+            <entry>serial line IP (slip)</entry>
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+          </row>
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+          <row>
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+            <entry><constant>wl</constant></entry>
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+            <entry>Wireless local area network (WLAN)</entry>
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+          </row>
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+          <row>
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+            <entry><constant>ww</constant></entry>
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+            <entry>Wireless wide area network (WWAN)</entry>
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+          </row>
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+        
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+      </tgroup>
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+    
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+
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+    <para>The udev <command>net_id</command> builtin exports the following udev device properties:</para>
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+
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+    <variablelist>
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+        <varlistentry>
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+          <term><varname>ID_NET_NAME_ONBOARD=<replaceable>prefix</replaceable><constant>o</constant><replaceable>number</replaceable></varname></term>
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+
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+          <listitem><para>This name is set based on the ordering information given by the firmware for
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+          on-board devices. The name consists of the prefix, letter <constant>o</constant>, and a number
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+          specified by the firmware. This is only available for PCI devices.</para>
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+          </listitem>
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+        </varlistentry>
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+
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+        <varlistentry>
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+          <term><varname>ID_NET_LABEL_ONBOARD=<replaceable>prefix</replaceable> <replaceable>label</replaceable></varname></term>
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+
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+          <listitem><para>This property is set based on label given by the firmware for on-board devices. The
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+          name consists of the prefix concatenated with the label. This is only available for PCI devices.
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+          </para>
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+          </listitem>
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+        </varlistentry>
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+
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+        <varlistentry>
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+          <term><varname>ID_NET_NAME_MAC=<replaceable>prefix</replaceable><constant>x</constant><replaceable>AABBCCDDEEFF</replaceable></varname></term>
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+
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+          <listitem><para>This name consists of the prefix, letter <constant>x</constant>, and 12 hexadecimal
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+          digits of the MAC address. It is available if the device has a fixed MAC address. Because this name
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+          is based on an attribute of the card itself, it remains "stable" when the device is moved (even
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+          between machines), but will change when the hardware is replaced.</para>
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+          </listitem>
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+        </varlistentry>
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+
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+        <varlistentry>
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+          <term><varname>ID_NET_NAME_SLOT=<replaceable>prefix</replaceable>[<constant>P</constant><replaceable>domain</replaceable>]<constant>s</constant><replaceable>slot</replaceable>[<constant>f</constant><replaceable>function</replaceable>][<constant>n</constant><replaceable>port_name</replaceable>|<constant>d</constant><replaceable>dev_port</replaceable>]</varname></term>
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+          <term><varname>ID_NET_NAME_SLOT=<replaceable>prefix</replaceable>[<constant>P</constant><replaceable>domain</replaceable>]<constant>s</constant><replaceable>slot</replaceable>[<constant>f</constant><replaceable>function</replaceable>][<constant>n</constant><replaceable>port_name</replaceable>|<constant>d</constant><replaceable>dev_port</replaceable>]<constant>b</constant><replaceable>number</replaceable></varname></term>
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+          <term><varname>ID_NET_NAME_SLOT=<replaceable>prefix</replaceable>[<constant>P</constant><replaceable>domain</replaceable>]<constant>s</constant><replaceable>slot</replaceable>[<constant>f</constant><replaceable>function</replaceable>][<constant>n</constant><replaceable>port_name</replaceable>|<constant>d</constant><replaceable>dev_port</replaceable>]<constant>u</constant><replaceable>port</replaceable>…[<constant>c</constant><replaceable>config</replaceable>][<constant>i</constant><replaceable>interface</replaceable>]</varname></term>
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+          <term><varname>ID_NET_NAME_SLOT=<replaceable>prefix</replaceable>[<constant>P</constant><replaceable>domain</replaceable>]<constant>s</constant><replaceable>slot</replaceable>[<constant>f</constant><replaceable>function</replaceable>][<constant>n</constant><replaceable>port_name</replaceable>|<constant>d</constant><replaceable>dev_port</replaceable>]<constant>v</constant><replaceable>slot</replaceable></varname></term>
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+
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+          <listitem><para>This property describes the slot position. Different schemes are used depending on
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+          the bus type, as described in the table below. In all cases, PCI slot information must be known. In
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+          case of USB, BCMA, and SR-VIO devices, the full name consists of the prefix, PCI slot identifier,
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+          and USB or BCMA or SR-VIO slot identifier. The first two parts are denoted as "…" in the table
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+          below.</para>
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+
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+          
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+            <title>Slot naming schemes</title>
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+
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+            <tgroup cols='2'>
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+              
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+                <row>
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+                  <entry>Format</entry>
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+                  <entry>Description</entry>
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+                </row>
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+              
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+
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+              
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+                <row>
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+                  <entry><replaceable>prefix</replaceable> [<constant>P</constant><replaceable>domain</replaceable>] <constant>s</constant><replaceable>slot</replaceable> [<constant>f</constant><replaceable>function</replaceable>] [<constant>n</constant><replaceable>port_name</replaceable> | <constant>d</constant><replaceable>dev_port</replaceable>]</entry>
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+                  <entry>PCI slot number</entry>
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+                </row>
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+
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+                <row>
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+                  <entry>… <constant>b</constant><replaceable>number</replaceable></entry>
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+                  <entry>Broadcom bus (BCMA) core number</entry>
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+                </row>
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+
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+                <row>
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+                  <entry>… <constant>u</constant><replaceable>port</replaceable>… [<constant>c</constant><replaceable>config</replaceable>] [<constant>i</constant><replaceable>interface</replaceable>]</entry>
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+                  <entry>USB port number chain</entry>
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+                </row>
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+
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+                <row>
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+                  <entry>… <constant>v</constant><replaceable>slot</replaceable></entry>
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+                  <entry>SR-VIO slot number</entry>
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+                </row>
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+              
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+            </tgroup>
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+          
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+
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+          <para>The PCI domain is only prepended when it is not 0. All multi-function PCI devices will carry
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+          the <constant>f<replaceable>function</replaceable></constant> number in the device name, including
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+          the function 0 device. For non-multi-function devices, the number is suppressed if 0. The port name
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+          <replaceable>port_name</replaceable> is used, or the port number
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+          <constant>d</constant><replaceable>dev_port</replaceable> if the name is not known.</para>
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+
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+          <para>For BCMA devices, the core number is suppressed when 0.</para>
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+
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+          <para>For USB devices the full chain of port numbers of hubs is composed. If the name gets longer
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+          than the maximum number of 15 characters, the name is not exported. The usual USB configuration
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+          number 1 and interface number 0 values are suppressed.</para>
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+          </listitem>
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+
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+          <para>SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of
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+          <constant>v</constant> and the virtual device number, with any leading zeros removed. The bus
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+          number is ignored. This device type is found in IBM PowerVMs.</para>
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+        </varlistentry>
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+
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+        <varlistentry>
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+          <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable><constant>c</constant><replaceable>bus_id</replaceable></varname></term>
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+          <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable><constant>a</constant><replaceable>vendor</replaceable><replaceable>model</replaceable><constant>i</constant><replaceable>instance</replaceable></varname></term>
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+          <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable><constant>i</constant><replaceable>address</replaceable><constant>n</constant><replaceable>port_name</replaceable></varname></term>
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+          <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable>[<constant>P</constant><replaceable>domain</replaceable>]<constant>p</constant><replaceable>bus</replaceable><constant>s</constant><replaceable>slot</replaceable>[<constant>f</constant><replaceable>function</replaceable>][<constant>n</constant><replaceable>phys_port_name</replaceable>|<constant>d</constant><replaceable>dev_port</replaceable>]</varname></term>
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+          <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable>[<constant>P</constant><replaceable>domain</replaceable>]<constant>p</constant><replaceable>bus</replaceable><constant>s</constant><replaceable>slot</replaceable>[<constant>f</constant><replaceable>function</replaceable>][<constant>n</constant><replaceable>phys_port_name</replaceable>|<constant>d</constant><replaceable>dev_port</replaceable>]<constant>b</constant><replaceable>number</replaceable></varname></term>
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+          <term><varname>ID_NET_NAME_PATH=<replaceable>prefix</replaceable>[<constant>P</constant><replaceable>domain</replaceable>]<constant>p</constant><replaceable>bus</replaceable><constant>s</constant><replaceable>slot</replaceable>[<constant>f</constant><replaceable>function</replaceable>][<constant>n</constant><replaceable>phys_port_name</replaceable>|<constant>d</constant><replaceable>dev_port</replaceable>]<constant>u</constant><replaceable>port</replaceable>…[<constant>c</constant><replaceable>config</replaceable>][<constant>i</constant><replaceable>interface</replaceable>]</varname></term>
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+
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+          <listitem><para>This property describes the device installation location. Different schemes are
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+          used depending on the bus type, as described in the table below. For BCMA and USB devices, PCI path
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+          information must known, and the full name consists of the prefix, PCI slot identifier, and USB or
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+          BCMA location. The first two parts are denoted as "…" in the table below.</para>
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+
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+          
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+            <title>Path naming schemes</title>
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+
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+            <tgroup cols='2'>
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+              
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+                <row>
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+                  <entry>Format</entry>
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+                  <entry>Description</entry>
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+                </row>
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+              
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+
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+              
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+                <row>
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+                  <entry><replaceable>prefix</replaceable> <constant>c</constant><replaceable>bus_id</replaceable></entry>
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+                  <entry>CCW or grouped CCW device identifier</entry>
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+                </row>
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+
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+                <row>
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+                  <entry><replaceable>prefix</replaceable> <constant>a</constant><replaceable>vendor</replaceable> <replaceable>model</replaceable> <constant>i</constant><replaceable>instance</replaceable></entry>
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+                  <entry>ACPI path names for ARM64 platform devices</entry>
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+                </row>
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+
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+                <row>
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+                  <entry><replaceable>prefix</replaceable> [<constant>P</constant><replaceable>domain</replaceable>] <constant>p</constant><replaceable>bus</replaceable> <constant>s</constant><replaceable>slot</replaceable> [<constant>f</constant><replaceable>function</replaceable>] [<constant>n</constant><replaceable>phys_port_name</replaceable> | <constant>d</constant><replaceable>dev_port</replaceable>]</entry>
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+                  <entry>PCI geographical location</entry>
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+                </row>
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+
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+                <row>
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+                  <entry>… <constant>b</constant><replaceable>number</replaceable></entry>
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+                  <entry>Broadcom bus (BCMA) core number</entry>
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+                </row>
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+
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+                <row>
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+                  <entry>… <constant>u</constant><replaceable>port</replaceable>… [<constant>c</constant><replaceable>config</replaceable>] [<constant>i</constant><replaceable>interface</replaceable>]</entry>
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+                  <entry>USB port number chain</entry>
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+                </row>
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+
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+              
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+            </tgroup>
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+          
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+
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+          <para>CCW and grouped CCW devices are found in IBM System Z mainframes. Any leading zeros and
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+          dots are suppressed.</para>
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+
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+          <para>For PCI, BCMA, and USB devices, the same rules as described above for slot naming are
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+          used.</para>
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+          </listitem>
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+        </varlistentry>
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+    </variablelist>
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+  </refsect1>
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+
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+  <refsect1>
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+    <title>History</title>
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+
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+    <para>The following "naming schemes" have been defined:</para>
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+
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+    <variablelist>
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+        <varlistentry>
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+          <term><constant>rhel-8.0</constant></term>
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+
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+          <listitem><para>Naming was changed for virtual network interfaces created with SR-IOV and NPAR and
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+          for devices where the PCI network controller device does not have a slot number associated.</para>
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+
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+          <para>SR-IOV virtual devices are named based on the name of the parent interface, with a suffix of
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+          <literal>v<replaceable>port</replaceable></literal>, where <replaceable>port</replaceable> is the
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+          virtual device number. Previously those virtual devices were named as if completely independent.
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+          </para>
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+
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+          <para>The ninth and later NPAR virtual devices are named following the scheme used for the first
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+          eight NPAR partitions. Previously those devices were not renamed and the kernel default
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+          ("eth<replaceable>N</replaceable>") was used.</para>
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+
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+          <para>Names are also generated for PCI devices where the PCI network controller device does not
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+          have an associated slot number itself, but one of its parents does. Previously those devices were
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+          not renamed and the kernel default was used.</para>
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+          </listitem>
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+        </varlistentry>
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+
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+        <varlistentry>
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+          <term><constant>rhel-8.1</constant></term>
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+
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+          <para>Same as naming scheme <constant>rhel-8.0</constant>.</para>
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+        </varlistentry>
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+
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+        <varlistentry>
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+          <term><constant>rhel-8.2</constant></term>
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+
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+          <para>Same as naming scheme <constant>rhel-8.0</constant>.</para>
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+        </varlistentry>
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+
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+        <varlistentry>
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+          <term><constant>rhel-8.3</constant></term>
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+
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+          <para>Same as naming scheme <constant>rhel-8.0</constant>.</para>
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+        </varlistentry>
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+
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+        <para>Note that <constant>latest</constant> may be used to denote the latest scheme known (to this
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+        particular version of systemd.</para>
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+    </variablelist>
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+  </refsect1>
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+
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+  <refsect1>
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+    <title>Examples</title>
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+
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+    <example>
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+      <title>Using <command>udevadm test-builtin</command> to display device properties</title>
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+
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+      <programlisting>$ udevadm test-builtin net_id /sys/class/net/enp0s31f6
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+...
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+Using default interface naming scheme 'rhel-8.3'.
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+ID_NET_NAMING_SCHEME=rhel-8.3
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+ID_NET_NAME_MAC=enx54ee75cb1dc0
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+ID_OUI_FROM_DATABASE=Wistron InfoComm(Kunshan)Co.,Ltd.
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+ID_NET_NAME_PATH=enp0s31f6
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+...</programlisting>
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+    </example>
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+
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+    <example>
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+      <title>PCI Ethernet card with firmware index "1"</title>
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+
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+      <programlisting>ID_NET_NAME_ONBOARD=eno1
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+ID_NET_NAME_ONBOARD_LABEL=enEthernet Port 1
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+      </programlisting>
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+      
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+    </example>
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+
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+    <example>
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+      <title>PCI Ethernet card in hotplug slot with firmware index number</title>
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+
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+      <programlisting># /sys/devices/pci0000:00/0000:00:1c.3/0000:05:00.0/net/ens1
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+ID_NET_NAME_MAC=enx000000000466
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+ID_NET_NAME_PATH=enp5s0
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+ID_NET_NAME_SLOT=ens1</programlisting>
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+    </example>
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+
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+    <example>
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+      <title>PCI Ethernet multi-function card with 2 ports</title>
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+
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+      <programlisting># /sys/devices/pci0000:00/0000:00:1c.0/0000:02:00.0/net/enp2s0f0
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+ID_NET_NAME_MAC=enx78e7d1ea46da
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+ID_NET_NAME_PATH=enp2s0f0
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+
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+# /sys/devices/pci0000:00/0000:00:1c.0/0000:02:00.1/net/enp2s0f1
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+ID_NET_NAME_MAC=enx78e7d1ea46dc
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+ID_NET_NAME_PATH=enp2s0f1</programlisting>
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+    </example>
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+
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+    <example>
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+      <title>PCI WLAN card</title>
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+
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+      <programlisting># /sys/devices/pci0000:00/0000:00:1c.1/0000:03:00.0/net/wlp3s0
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+ID_NET_NAME_MAC=wlx0024d7e31130
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+ID_NET_NAME_PATH=wlp3s0</programlisting>
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+    </example>
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+
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+    <example>
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+      <title>USB built-in 3G modem</title>
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+
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+      <programlisting># /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.4/2-1.4:1.6/net/wwp0s29u1u4i6
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+ID_NET_NAME_MAC=wwx028037ec0200
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+ID_NET_NAME_PATH=wwp0s29u1u4i6</programlisting>
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+    </example>
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+
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+    <example>
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+      <title>USB Android phone</title>
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+
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+      <programlisting># /sys/devices/pci0000:00/0000:00:1d.0/usb2/2-1/2-1.2/2-1.2:1.0/net/enp0s29u1u2
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+ID_NET_NAME_MAC=enxd626b3450fb5
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+ID_NET_NAME_PATH=enp0s29u1u2</programlisting>
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+    </example>
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+
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+    <example>
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+      <title>s390 grouped CCW interface</title>
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+
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+      <programlisting># /sys/devices/css0/0.0.0007/0.0.f5f0/group_device/net/encf5f0
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+ID_NET_NAME_MAC=enx026d3c00000a
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+ID_NET_NAME_PATH=encf5f0</programlisting>
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+    </example>
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+  </refsect1>
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+
87d178
+  <refsect1>
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+    <title>See Also</title>
87d178
+    <para>
87d178
+      <citerefentry><refentrytitle>udev</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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+      <citerefentry><refentrytitle>udevadm</refentrytitle><manvolnum>8</manvolnum></citerefentry>,
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+      <ulink url="https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames">the
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+      original page describing stable interface names</ulink>
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+    </para>
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+  </refsect1>
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+
87d178
+</refentry>
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diff --git a/src/udev/udev-builtin-net_id.c b/src/udev/udev-builtin-net_id.c
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index d85dc2848b..aa553d5ade 100644
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--- a/src/udev/udev-builtin-net_id.c
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+++ b/src/udev/udev-builtin-net_id.c
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@@ -78,6 +78,7 @@
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  *  /sys/devices/css0/0.0.0007/0.0.f5f0/group_device/net/encf5f0
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  *  ID_NET_NAME_MAC=enx026d3c00000a
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  *  ID_NET_NAME_PATH=encf5f0
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+ * When the code here is changed, man/systemd.net-naming-scheme.xml must be updated too.
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  */
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87d178
 #include <errno.h>