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>

1 files changed, 17 insertions, 1 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)