particular version of systemd).</para>
</refsect1>
+ <refsect1>
+ <title>Limiting the use of specific sysfs attributes</title>
+
+ <para>When creating names for network cards, some naming schemes use data from sysfs populated
+ by the kernel. This means that although a specific naming scheme in udev is picked,
+ the network card's name can still change when a new kernel version adds a new sysfs attribute.
+ For example if kernel starts setting the <constant>phys_port_name</constant>, udev will append the
+ "<constant>n</constant><replaceable>phys_port_name</replaceable>" suffix to the device name.</para>
+
+ <variablelist>
+ <varlistentry>
+ <term><varname>ID_NET_NAME_ALLOW=<replaceable>BOOL</replaceable></varname></term>
+
+ <listitem><para>This evironment value sets a fallback policy for reading a sysfs attribute.
+ If set to <constant>0</constant> udev will not read any sysfs attribute by default, unless it is
+ explicitly allowlisted, see below. If set to <constant>1</constant> udev can use any sysfs attribute
+ unless it is explicitly forbidden. The default value is <constant>1</constant>.</para>
+
+ <xi:include href="version-info.xml" xpointer="v256"/>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>ID_NET_NAME_ALLOW_<replaceable>sysfsattr</replaceable>=<replaceable>BOOL</replaceable></varname></term>
+
+ <listitem><para>This evironment value explicitly states if udev shall use the specified
+ <replaceable>sysfsattr</replaceable>, when composing the device name.</para>
+
+ <xi:include href="version-info.xml" xpointer="v256"/>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+
+ <para>With these options, users can set an allowlist or denylist for sysfs attributes. To create
+ an allowlist, the user needs to set <varname>ID_NET_NAME_ALLOW=0</varname> for the device and then list
+ the allowed attributes with the
+ <varname>ID_NET_NAME_ALLOW_<replaceable>sysfsattr</replaceable>=1</varname>
+ options. In case of a denylist, the user needs to provide the list of denied attributes with
+ the <varname>ID_NET_NAME_ALLOW_<replaceable>sysfsattr</replaceable>=0</varname> options.</para>
+ </refsect1>
+
<refsect1>
<title>Examples</title>
ID_NET_NAME_MAC=enx026d3c00000a
ID_NET_NAME_PATH=encf5f0</programlisting>
</example>
+
+ <example>
+ <title>Set an allowlist for reading sysfs attributes for network card naming</title>
+
+ <programlisting><filename>/etc/udev/hwdb.d/50-net-naming-allowlist.hwdb</filename>
+net:naming:drvirtio_net:*
+ ID_NET_NAME_ALLOW=0
+ ID_NET_NAME_ALLOW_ACPI_INDEX=1
+ ID_NET_NAME_ALLOW_ADDR_ASSIGN_TYPE=1
+ ID_NET_NAME_ALLOW_ADDRESS=1
+ ID_NET_NAME_ALLOW_ARI_ENABLED=1
+ ID_NET_NAME_ALLOW_DEV_PORT=1
+ ID_NET_NAME_ALLOW_FUNCTION_ID=1
+ ID_NET_NAME_ALLOW_IFLINK=1
+ ID_NET_NAME_ALLOW_INDEX=1
+ ID_NET_NAME_ALLOW_LABEL=1
+ ID_NET_NAME_ALLOW_PHYS_PORT_NAME=1
+ ID_NET_NAME_ALLOW_TYPE=1</programlisting>
+ </example>
+
+ <example>
+ <title>Set a denylist so that specified sysfs attribute are ignored</title>
+
+ <programlisting><filename>/etc/udev/hwdb.d/50-net-naming-denylist.hwdb</filename>
+net:naming:drvirtio_net:*
+ ID_NET_NAME_ALLOW=1
+ ID_NET_NAME_ALLOW_DEV_PORT=0
+ ID_NET_NAME_ALLOW_PHYS_PORT_NAME=0
+ </programlisting>
+ </example>
</refsect1>
<refsect1>