confd: ethtool: Condense logic around autoneg configuration

Rely on the interface diff to figure out if any autoneg related config
has changed; if so, generate the resulting configuration based on the
current interface config.

- Remove loopback check, the model only allows ethernet config on
  interfaces of type "ethernet".

- Split up the input validation of speed/duplex to give the user an
  error message with as much specificity as possible.

- Validate that the configured speed/duplex is supported.

- Move the generated script to execute earlier to avoid unnecessary
  link flapping.

- Use negative POSIX error codes, these are (or at least should be)
  mapped to sysrepo errors in netdag_gen_iface.

src/confd/src/ietf-interfaces.c

@@ -653,6 +653,76 @@ skip_mtu:
 	return err;
 }
 
+static int netdag_gen_ethtool_autoneg(struct dagger *net, struct lyd_node *cif)
+{
+	struct lyd_node *eth = lydx_get_child(cif, "ethernet");
+	struct lyd_node *aneg = lydx_get_child(eth, "auto-negotiation");
+	const char *ifname = lydx_get_cattr(cif, "name");
+	const char *speed, *duplex;
+	int mbps, err = 0;
+	FILE *fp;
+
+	fp = dagger_fopen_next(net, "init", ifname, 10, "ethtool-aneg.sh");
+	if (!fp)
+		return -EIO;
+
+	fprintf(fp, "ethtool --change %s autoneg ", ifname);
+
+	if (!aneg || lydx_is_enabled(aneg, "enable")) {
+		fputs("on\n", fp);
+	} else {
+		speed = lydx_get_cattr(eth, "speed");
+		if (!speed) {
+			sr_session_set_error_message(net->session, "%s: "
+						     "\"speed\" must be specified "
+						     "when auto-negotiation is disabled", ifname);
+			err = -EINVAL;
+			goto out;
+		}
+
+		mbps = (int)(atof(speed) * 1000.);
+		if (!((mbps == 10) || (mbps == 100))) {
+				sr_session_set_error_message(net->session, "%s: "
+						     "\"speed\" must be either 0.01 or 0.1 "
+						     "when auto-negotiation is disabled", ifname);
+			err = -EINVAL;
+			goto out;
+		}
+
+		duplex = lydx_get_cattr(eth, "duplex");
+		if (!duplex || (strcmp(duplex, "full") && strcmp(duplex, "half"))) {
+			sr_session_set_error_message(net->session, "%s: "
+						     "\"duplex\" must be either "
+						     "\"full\" or \"half\" "
+						     "when auto-negotiation is disabled", ifname);
+			err = -EINVAL;
+			goto out;
+		}
+
+		fprintf(fp,"off speed %d duplex %s\n", mbps, duplex);
+	}
+out:
+	fclose(fp);
+	return err;
+
+}
+
+static int netdag_gen_ethtool(struct dagger *net, struct lyd_node *cif, struct lyd_node *dif)
+{
+	struct lyd_node *eth = lydx_get_child(dif, "ethernet");
+	int err;
+
+	if (lydx_get_descendant(lyd_child(eth), "auto-negotiation", "enable", NULL) ||
+	    lydx_get_child(eth, "speed") ||
+	    lydx_get_child(eth, "duplex")) {
+		err = netdag_gen_ethtool_autoneg(net, cif);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
 static int bridge_diff_vlan_port(struct dagger *net, FILE *br, const char *brname, int vid,
 				       const char *brport, int tagged, enum lydx_op op)
 {
@@ -1140,6 +1210,8 @@ static sr_error_t netdag_gen_iface(struct dagger *net,
 
 	err = err ? : netdag_gen_sysctl(net, cif, dif);
 
+	err = err ? : netdag_gen_ethtool(net, cif, dif);
+
 err_close_ip:
 	fclose(ip);
 err: