add a config option to disable automatically setting the dhcp hostname

dist/ifupdown-ng.conf.example

@@ -24,3 +24,10 @@ allow_any_iface_as_template = 1
 # work against non-template interfaces without converting them to a
 # template.  Valid values are 0 and 1, the default is 1.
 implicit_template_conversion = 1
+
+# use_hostname_for_dhcp:
+# Automatically learn the hostname property, used for DHCP configuration
+# by querying the system hostname using uname(2).  This is basically
+# equivalent to `hostname $(hostname)` without having to specify any
+# configuration.  Valid values are 0 and 1, the default is 1.
+use_hostname_for_dhcp = 1

libifupdown/config-file.c

@@ -22,6 +22,7 @@ struct lif_config_file lif_config = {
 	.allow_addon_scripts = true,
 	.allow_any_iface_as_template = true,
 	.implicit_template_conversion = true,
+	.use_hostname_for_dhcp = true,
 };
 
 static bool
@@ -47,6 +48,7 @@ static struct lif_config_handler handlers[] = {
 	{"allow_addon_scripts", set_bool_value, &lif_config.allow_addon_scripts},
 	{"allow_any_iface_as_template", set_bool_value, &lif_config.allow_any_iface_as_template},
 	{"implicit_template_conversion", set_bool_value, &lif_config.implicit_template_conversion},
+	{"use_hostname_for_dhcp", set_bool_value, &lif_config.use_hostname_for_dhcp},
 };
 
 bool

libifupdown/config-file.h

@@ -22,6 +22,7 @@ struct lif_config_file {
 	bool allow_addon_scripts;
 	bool allow_any_iface_as_template;
 	bool implicit_template_conversion;
+	bool use_hostname_for_dhcp;
 };
 
 extern struct lif_config_file lif_config;

libifupdown/interface.c

@@ -123,6 +123,9 @@ lif_interface_init(struct lif_interface *interface, const char *ifname)
 	if (strchr(ifname, '.') != NULL)
 		lif_interface_use_executor(interface, "vlan");
 
+	if (!lif_config.use_hostname_for_dhcp)
+		return;
+
 	/* learn a reasonable default hostname */
 	struct utsname un;
 	if (uname(&un) < 0)