udhcpc6: add ELAPSED_TIME option to outgoing packets

function                                             old     new   delta
init_d6_packet                                        53     121     +68
udhcpc_main                                         2577    2582      +5
udhcpc6_main                                        2593    2597      +4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 77/0)               Total: 77 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

3 files changed, 21 insertions, 5 deletions

diff --git a/networking/udhcp/d6_dhcpc.c b/networking/udhcp/d6_dhcpc.c
index a426b9933..85c410a7c 100644
--- a/networking/udhcp/d6_dhcpc.c
+++ b/networking/udhcp/d6_dhcpc.c
@@ -481,15 +481,31 @@ static ALWAYS_INLINE uint32_t random_xid(void)
 /* Initialize the packet with the proper defaults */
 static uint8_t *init_d6_packet(struct d6_packet *packet, char type, uint32_t xid)
 {
+	uint8_t *ptr;
 	struct d6_option *clientid;
+	unsigned secs;
 
 	memset(packet, 0, sizeof(*packet));
 
 	packet->d6_xid32 = xid;
 	packet->d6_msg_type = type;
 
+	/* ELAPSED_TIME option is required to be present by the RFC,
+	 * and some servers do check for its presense. [which?]
+	 */
+	ptr = packet->d6_options; /* NB: it is 32-bit aligned */
+	*((uint32_t*)ptr) = htonl((D6_OPT_ELAPSED_TIME << 16) + 2);
+	ptr += 4;
+	client_data.last_secs = monotonic_sec();
+	if (client_data.first_secs == 0)
+		client_data.first_secs = client_data.last_secs;
+	secs = client_data.last_secs - client_data.first_secs;
+	*((uint16_t*)ptr) = (secs < 0xffff) ? htons(secs) : 0xffff;
+	ptr += 2;
+
+	/* add CLIENTID option */
 	clientid = (void*)client_data.clientid;
-	return mempcpy(packet->d6_options, clientid, clientid->len + 2+2);
+	return mempcpy(ptr, clientid, clientid->len + 2+2);
 }
 
 static uint8_t *add_d6_client_options(uint8_t *ptr)
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index 656295ff7..5a1f8fd7a 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -606,7 +606,7 @@ static ALWAYS_INLINE uint32_t random_xid(void)
 /* Initialize the packet with the proper defaults */
 static void init_packet(struct dhcp_packet *packet, char type)
 {
-	uint16_t secs;
+	unsigned secs;
 
 	/* Fill in: op, htype, hlen, cookie fields; message type option: */
 	udhcp_init_header(packet, type);
@@ -617,7 +617,7 @@ static void init_packet(struct dhcp_packet *packet, char type)
 	if (client_data.first_secs == 0)
 		client_data.first_secs = client_data.last_secs;
 	secs = client_data.last_secs - client_data.first_secs;
-	packet->secs = htons(secs);
+	packet->secs = (secs < 0xffff) ? htons(secs) : 0xffff;
 
 	memcpy(packet->chaddr, client_data.client_mac, 6);
 	if (client_data.clientid)
diff --git a/networking/udhcp/dhcpc.h b/networking/udhcp/dhcpc.h
index 42fe71a36..b407a6cdb 100644
--- a/networking/udhcp/dhcpc.h
+++ b/networking/udhcp/dhcpc.h
@@ -22,8 +22,8 @@ struct client_data_t {
 	uint8_t *hostname;              /* Optional hostname to use */
 	uint8_t *fqdn;                  /* Optional fully qualified domain name to use */
 
-	uint16_t first_secs;
-	uint16_t last_secs;
+	unsigned first_secs;
+	unsigned last_secs;
 
 	int sockfd;
 	smallint listen_mode;