netd: get dns server from dhcp

tools/netd/main.c

@@ -13,6 +13,8 @@
 #include <errno.h>
 #include <poll.h>
 #include <net/route.h>
+#include <fcntl.h>
+#include <unistd.h>
 
 #ifndef SIOCADDRT
 	#define SIOCADDRT	0x890B
@@ -57,10 +59,11 @@ typedef struct {
 #define OPTION_TYPE_DHCPACK 5
 
 #define OPTION_REQUEST 55
-#define OPTION_REQUEST_LENGTH 2
+#define OPTION_REQUEST_LENGTH 3
 
 #define OPTION_MASK 1
 #define OPTION_ROUTER 3
+#define OPTION_DNS 6
 #define OPTION_LEASETIME 51
 #define OPTION_IPREQ 50
 #define OPTION_SERVER 54
@@ -68,7 +71,7 @@ typedef struct {
 
 static uint8_t discoveropts[] = {
 	OPTION_TYPE, OPTION_TYPE_LENGTH, OPTION_TYPE_DHCPDISCOVER,
-	OPTION_REQUEST, OPTION_REQUEST_LENGTH, OPTION_MASK, OPTION_ROUTER,
+	OPTION_REQUEST, OPTION_REQUEST_LENGTH, OPTION_MASK, OPTION_ROUTER, OPTION_DNS,
 	0xff
 };
 
@@ -223,6 +226,7 @@ typedef struct {
 	uint32_t netmask;
 	uint32_t router;
 	uint32_t leasetime;
+	uint32_t dns;
 } offer_t;
 
 static int processoffer(offer_t *offer, uint32_t *xid) {
@@ -271,6 +275,10 @@ static int processoffer(offer_t *offer, uint32_t *xid) {
 				uint32_t leasetime = optget32(opts, i + 2);
 				offer->leasetime = leasetime;
 				break;
+			case OPTION_DNS:
+				uint32_t dns = optget32(opts, i + 2);
+				offer->dns = dns;
+				break;
 			case OPTION_END:
 				goto leave;
 		}
@@ -381,6 +389,7 @@ static void printoffer(offer_t *offer) {
 	printip("server ip", offer->serverip);
 	printip("netmask", offer->netmask);
 	printip("router", offer->router);
+	printip("DNS", offer->dns);
 	printf("%s: lease time: %d seconds\n", name, offer->leasetime);
 }
 
@@ -422,6 +431,28 @@ static void setifip(char *device, uint32_t addr) {
 		logstrerror("failed to set device ip address");
 }
 
+static void writedns(uint32_t dns) {
+	char buff[100];
+	int fd = creat("/etc/resolv.conf", 0644);
+	if (fd < 0) {
+		perror("failed to create /etc/resolv.conf");
+		return;
+	}
+
+	struct in_addr addr;
+	addr.s_addr = htonl(dns);
+	char *ipstr = inet_ntoa(addr);
+	
+	snprintf(buff, 100, "# generated by netd\nnameserver %s\n", ipstr);
+
+	if (write(fd, buff, strlen(buff)) < 0) {
+		perror("failed to write to /etc/resolv.conf");
+		return;
+	}
+
+	close(fd);
+}
+
 int main(int argc, char *argv[]) {
 	name = argv[0];
 
@@ -486,6 +517,7 @@ int main(int argc, char *argv[]) {
 	addroute(argv[1], 0, offer.router, 0, 1);
 	addroute(argv[1], offer.clientip, 0, offer.netmask, 10);
 	setifip(argv[1], offer.clientip);
+	writedns(offer.dns);
 
 	return EXIT_SUCCESS;
 }