confd: infer default DHCP client options

For maximum flexibility we allow the user to full control over the DHCP
options the client requests.  For this to work we must tell udhcpc to
not set any of its defaults behind the scenes, so we call it with '-o'.

This commit adds support for inferring these udhcpc default options in
NETCONF.  So when enabling the DHCP client we now get the same set of
sane options as udhcpc otherwise hides from us.

Fixes #278, at least wrt. the lack of sent options.  Allowing the client
script to set the hostname will be added in a later commit.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/confd/src/infix-dhcp.c

@@ -344,6 +344,76 @@ err_abandon:
 	return err;
 }
 
+/*
+ * Default DHCP options for udhcpc, from networking/udhcp/common.c OPTION_REQ
+ */
+static void infer_options(sr_session_ctx_t *session, const char *xpath)
+{
+	const char *opt[] = {
+		"subnet",
+		"router",
+		"dns",
+		"hostname", /* server may use this to register our current name */
+		"domain",
+		"broadcast",
+		"ntpsrv"    /* will not be activated unless ietf-system also is */
+	};
+	size_t i;
+
+	for (i = 0; i < NELEMS(opt); i++)
+		srx_set_item(session, NULL, 0, "%s/option[name='%s']", xpath, opt[i]);
+}
+
+static int cand(sr_session_ctx_t *session, uint32_t sub_id, const char *module,
+		const char *xpath, sr_event_t event, unsigned request_id, void *priv)
+{
+	sr_change_iter_t *iter;
+	sr_change_oper_t op;
+	sr_val_t *old, *new;
+	sr_error_t err;
+
+	switch (event) {
+	case SR_EV_UPDATE:
+	case SR_EV_CHANGE:
+		break;
+	default:
+		return SR_ERR_OK;
+	}
+
+	err = sr_dup_changes_iter(session, XPATH "/client-if//*", &iter);
+	if (err)
+		return err;
+
+	while (sr_get_change_next(session, iter, &op, &old, &new) == SR_ERR_OK) {
+		char xpath[strlen(new->xpath) + 42];
+		size_t cnt = 0;
+		char *ptr;
+
+		switch (op) {
+		case SR_OP_CREATED:
+		case SR_OP_MODIFIED:
+			break;
+		default:
+			continue;
+		}
+
+		strlcpy(xpath, new->xpath, sizeof(xpath));
+		if ((ptr = strstr(xpath, "]/")) == NULL)
+			continue;
+		ptr[1] = 0;
+
+		err = srx_nitems(session, &cnt, "%s/option", xpath);
+		if (err || cnt) {
+			continue;
+		}
+
+		infer_options(session, xpath);
+	}
+
+	sr_free_change_iter(iter);
+	return SR_ERR_OK;
+}
+
 int infix_dhcp_init(struct confd *confd)
 {
 	int rc;
@@ -353,6 +423,8 @@ int infix_dhcp_init(struct confd *confd)
 		goto fail;
 
 	REGISTER_CHANGE(confd->session, MODULE, XPATH, 0, change, confd, &confd->sub);
+	REGISTER_CHANGE(confd->cand, MODULE, XPATH"//.", SR_SUBSCR_UPDATE, cand, confd, &confd->sub);
+
 	return SR_ERR_OK;
 fail:
 	ERROR("init failed: %s", sr_strerror(rc));