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network: dhcp-server: make empty string to DNS= or friends clear previously specified servers

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This commit is contained in:
Yu Watanabe 2022-02-02 07:20:25 +09:00
parent 32f8a613c5
commit faa1b3c6c4
2 changed files with 21 additions and 11 deletions
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26
man/systemd.network.xml
View file

@ -2561,17 +2561,21 @@ Token=prefixstable:2002:da8:1::</programlisting></para>
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, or special value <literal>_server_address</literal> which
will be converted to the address used by the DHCP server. 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 uplink 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>
will be converted to the address used by the DHCP server.</para>
<para>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 uplink 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>
<para>This setting can be specified multiple times. If an empty string is specified, then all
DNS servers specified earlier are cleared.</para></listitem>
</varlistentry>
<varlistentry>

6
src/network/networkd-dhcp-server.c
View file

@ -634,6 +634,12 @@ int config_parse_dhcp_server_emit(
assert(emit);
assert(rvalue);
if (isempty(rvalue)) {
emit->addresses = mfree(emit->addresses);
emit->n_addresses = 0;
return 0;
}
for (const char *p = rvalue;;) {
_cleanup_free_ char *w = NULL;
union in_addr_union a;