network: clean-up DHCP lease server data configuration

This is an attempt to clean up the POP3/SMTP/LPR/… DHCP lease server
data logic in networkd. This reduces code duplication and fixes a number
of bugs.

This removes any support for collecting POP3/SMPT/LPR servers acquired
via local DHCP client releases since noone uses that, and given how old
these protocols are I doubt this will change. It keeps support for
configuring them for the dhcp server however.

The differences between the DNS/NTP/SIP/POP3/SMTP/LPR configuration
logics are minimized.

This removes the relevant symbols from sd-network.h (which is an
internal API only at this point after all).

This is unfortunately not well test, given the old code for this had
barely any tests. But the new code should not perform worse at least,
and allow us to release, since it corrects some interfaces visible in
the .network configuration format.

Fixes: #15943

1 files changed, 29 insertions, 72 deletions

diff --git a/man/systemd.network.xml b/man/systemd.network.xml
index 851570e723..c0d8d979e6 100644
--- a/man/systemd.network.xml
+++ b/man/systemd.network.xml
@@ -578,7 +578,7 @@
         <varlistentry>
           <term><varname>NTP=</varname></term>
           <listitem>
-            <para>An NTP server address. This option may be specified more than once. This setting is read by
+            <para>An NTP server address (either an IP address, or a hostname). This option may be specified more than once. This setting is read by
             <citerefentry><refentrytitle>systemd-timesyncd.service</refentrytitle><manvolnum>8</manvolnum></citerefentry>.</para>
           </listitem>
         </varlistentry>
@@ -1412,17 +1412,16 @@
         <varlistentry>
           <term><varname>UseNTP=</varname></term>
           <listitem>
-            <para>When true (the default), the NTP servers received
-            from the DHCP server will be used by systemd-timesyncd
-            and take precedence over any statically configured ones.</para>
+            <para>When true (the default), the NTP servers received from the DHCP server will be used by
+            <filename>systemd-timesyncd.service</filename> and take precedence over any statically configured
+            ones.</para>
           </listitem>
         </varlistentry>
         <varlistentry>
           <term><varname>UseSIP=</varname></term>
           <listitem>
-            <para>When true (the default), the SIP servers received
-            from the DHCP server will be saved at the state files and can be
-            read via <function>sd_network_link_get_sip_servers()</function> function.</para>
+            <para>When true (the default), the SIP servers received from the DHCP server will be collected
+            and made available to client programs.</para>
           </listitem>
         </varlistentry>
 
@@ -2010,79 +2009,37 @@
         <term><varname>EmitDNS=</varname></term>
         <term><varname>DNS=</varname></term>
 
-        <listitem><para>Takes a boolean. Configures whether the DHCP leases handed out
-        to clients shall contain DNS server information. Defaults to <literal>yes</literal>.
-        The DNS servers to pass to clients may be configured with the
-        <varname>DNS=</varname> option, which takes a list of IPv4
-        addresses. If the <varname>EmitDNS=</varname> option is
-        enabled but no servers configured, the servers are
-        automatically propagated from an "uplink" interface that has
-        appropriate servers set. The "uplink" interface is determined
-        by the default route of the system with the highest
-        priority. Note that this information is acquired at the time
-        the lease is handed out, and does not take uplink interfaces
-        into account that acquire DNS or NTP server information at a
-        later point. DNS server propagation does not take
-        <filename>/etc/resolv.conf</filename> into account. Also, note
-        that the leases are not refreshed if the uplink network
-        configuration changes. To ensure clients regularly acquire the
-        most current uplink DNS server information, it is thus
-        advisable to shorten the DHCP lease time via
-        <varname>MaxLeaseTimeSec=</varname> described
+        <listitem><para><varname>EmitDNS=</varname> takes a boolean. Configures whether the DHCP leases
+        handed out to clients shall contain DNS server information. Defaults to <literal>yes</literal>.  The
+        DNS servers to pass to clients may be configured with the <varname>DNS=</varname> option, which takes
+        a list of IPv4 addresses. If the <varname>EmitDNS=</varname> option is enabled but no servers
+        configured, the servers are automatically propagated from an "uplink" interface that has appropriate
+        servers set. The "uplink" interface is determined by the default route of the system with the highest
+        priority. Note that this information is acquired at the time the lease is handed out, and does not
+        take uplink interfaces into account that acquire DNS server information at a later point. If no
+        suitable uplinkg interface is found the DNS server data from <filename>/etc/resolv.conf</filename> is
+        used. Also, note that the leases are not refreshed if the uplink network configuration changes. To
+        ensure clients regularly acquire the most current uplink DNS server information, it is thus advisable
+        to shorten the DHCP lease time via <varname>MaxLeaseTimeSec=</varname> described
         above.</para></listitem>
       </varlistentry>
 
       <varlistentry>
         <term><varname>EmitNTP=</varname></term>
         <term><varname>NTP=</varname></term>
-
-        <listitem><para>Similar to the <varname>EmitDNS=</varname> and
-        <varname>DNS=</varname> settings described above, these
-        settings configure whether and what NTP server information
-        shall be emitted as part of the DHCP lease. The same syntax,
-        propagation semantics and defaults apply as for
-        <varname>EmitDNS=</varname> and
-        <varname>DNS=</varname>.</para></listitem>
-      </varlistentry>
-
-      <varlistentry>
         <term><varname>EmitSIP=</varname></term>
         <term><varname>SIP=</varname></term>
-
-        <listitem><para>Similar to the <varname>EmitDNS=</varname> and
-        <varname>DNS=</varname> settings described above, these
-        settings configure whether and what SIP server information
-        shall be emitted as part of the DHCP lease. The same syntax,
-        propagation semantics and defaults apply as for
-        <varname>EmitDNS=</varname> and
-        <varname>DNS=</varname>.</para></listitem>
-      </varlistentry>
-
-      <varlistentry>
-        <term><varname>POP3Servers=</varname></term>
-
-        <listitem><para>Similar to the <varname>DNS=</varname> setting described above, this setting
-        configures whether and what POP3 server information shall be emitted as part of the DHCP lease. The
-        same syntax, propagation semantics and defaults apply as for
-        <varname>DNS=</varname>.</para></listitem>
-      </varlistentry>
-
-      <varlistentry>
-        <term><varname>SMTPServers=</varname></term>
-
-        <listitem><para>Similar to the <varname>DNS=</varname> setting described above, this
-        setting configures whether and what SMTP server information shall be emitted as part of
-        the DHCP lease. The same syntax, propagation semantics and defaults apply as for
-        <varname>DNS=</varname>.</para></listitem>
-      </varlistentry>
-
-      <varlistentry>
-        <term><varname>LPRServers=</varname></term>
-
-        <listitem><para>Similar to the <varname>DNS=</varname> setting described above, this
-        setting configures whether and what LPR (line printer) server information shall be emitted
-        as part of the DHCP lease. The same syntax, propagation semantics and defaults apply as for
-        <varname>DNS=</varname>.</para></listitem>
+        <term><varname>EmitPOP3=</varname></term>
+        <term><varname>POP3=</varname></term>
+        <term><varname>EmitSMTP=</varname></term>
+        <term><varname>SMTP=</varname></term>
+        <term><varname>EmitLPR=</varname></term>
+        <term><varname>LPR=</varname></term>
+
+        <listitem><para>Similar to the <varname>EmitDNS=</varname> and <varname>DNS=</varname> settings
+        described above, these settings configure whether and what server information for the indicate
+        protocol shall be emitted as part of the DHCP lease. The same syntax, propagation semantics and
+        defaults apply as for <varname>EmitDNS=</varname> and <varname>DNS=</varname>.</para></listitem>
       </varlistentry>
 
       <varlistentry>