udhcpd: add option for tweaking arpping

Some clients have a very short timeout for sending the DHCP
DISCOVER, shorter than the arpping timeout of 2000 milliseconds
that udhcpd uses by default.

This patch allows tweaking the timeout, or disabling of arpping
altogether, at the risk of handing out addresses which are
already in use.

function                                             old     new   delta
udhcpd_main                                         1460    1501     +41
udhcpc_main                                         2814    2851     +37
packed_usage                                       29957   29974     +17
arpping                                              477     493     +16
find_free_or_expired_nip                             161     174     +13
send_offer                                           285     292      +7
nobody_responds_to_arp                                85      89      +4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 7/0 up/down: 135/0)             Total: 135 bytes

Signed-off-by: Michel Stam <m.stam@fugro.nl>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

6 files changed, 39 insertions, 21 deletions

diff --git a/networking/udhcp/arpping.c b/networking/udhcp/arpping.c
index b43e52e96..fad2283c3 100644
--- a/networking/udhcp/arpping.c
+++ b/networking/udhcp/arpping.c
@@ -39,7 +39,8 @@ int FAST_FUNC arpping(uint32_t test_nip,
                 const uint8_t *safe_mac,
                 uint32_t from_ip,
                 uint8_t *from_mac,
-                const char *interface)
+                const char *interface,
+                unsigned timeo)
 {
         int timeout_ms;
         struct pollfd pfd[1];
@@ -48,6 +49,9 @@ int FAST_FUNC arpping(uint32_t test_nip,
         struct sockaddr addr;   /* for interface name */
         struct arpMsg arp;
 
+        if (!timeo)
+                return 1;
+
         s = socket(PF_PACKET, SOCK_PACKET, htons(ETH_P_ARP));
         if (s == -1) {
                 bb_perror_msg(bb_msg_can_not_create_raw_socket);
@@ -83,7 +87,7 @@ int FAST_FUNC arpping(uint32_t test_nip,
         }
 
         /* wait for arp reply, and check it */
-        timeout_ms = 2000;
+        timeout_ms = (int)timeo;
         do {
                 typedef uint32_t aliased_uint32_t FIX_ALIASING;
                 int r;
@@ -124,7 +128,7 @@ int FAST_FUNC arpping(uint32_t test_nip,
                  * this is more under/overflow-resistant
                  * (people did see overflows here when system time jumps):
                  */
-        } while ((unsigned)timeout_ms <= 2000);
+        } while ((unsigned)timeout_ms <= timeo);
 
  ret:
         close(s);
diff --git a/networking/udhcp/common.h b/networking/udhcp/common.h
index e5e0f2599..d20659e2f 100644
--- a/networking/udhcp/common.h
+++ b/networking/udhcp/common.h
@@ -311,7 +311,8 @@ int arpping(uint32_t test_nip,
                 const uint8_t *safe_mac,
                 uint32_t from_ip,
                 uint8_t *from_mac,
-                const char *interface) FAST_FUNC;
+                const char *interface,
+                unsigned timeo) FAST_FUNC;
 
 /* note: ip is a pointer to an IPv6 in network order, possibly misaliged */
 int sprint_nip6(char *dest, /*const char *pre,*/ const uint8_t *ip) FAST_FUNC;
diff --git a/networking/udhcp/dhcpc.c b/networking/udhcp/dhcpc.c
index e468b7bbb..35e7c2070 100644
--- a/networking/udhcp/dhcpc.c
+++ b/networking/udhcp/dhcpc.c
@@ -54,7 +54,7 @@ static const char udhcpc_longopts[] ALIGN1 =
         "foreground\0"     No_argument       "f"
         "background\0"     No_argument       "b"
         "broadcast\0"      No_argument       "B"
-        IF_FEATURE_UDHCPC_ARPING("arping\0"     No_argument       "a")
+        IF_FEATURE_UDHCPC_ARPING("arping\0"     Optional_argument "a")
         IF_FEATURE_UDHCP_PORT("client-port\0"   Required_argument "P")
         ;
 #endif
@@ -1150,7 +1150,7 @@ static void client_background(void)
 //usage:# define IF_UDHCP_VERBOSE(...)
 //usage:#endif
 //usage:#define udhcpc_trivial_usage
-//usage:       "[-fbq"IF_UDHCP_VERBOSE("v")IF_FEATURE_UDHCPC_ARPING("a")"RB] [-t N] [-T SEC] [-A SEC/-n]\n"
+//usage:       "[-fbq"IF_UDHCP_VERBOSE("v")"RB]"IF_FEATURE_UDHCPC_ARPING(" [-a[MSEC]]")" [-t N] [-T SEC] [-A SEC/-n]\n"
 //usage:       "        [-i IFACE]"IF_FEATURE_UDHCP_PORT(" [-P PORT]")" [-s PROG] [-p PIDFILE]\n"
 //usage:       "        [-oC] [-r IP] [-V VENDOR] [-F NAME] [-x OPT:VAL]... [-O OPT]..."
 //usage:#define udhcpc_full_usage "\n"
@@ -1174,7 +1174,7 @@ static void client_background(void)
 //usage:        )
 //usage:     "\n        -S,--syslog             Log to syslog too"
 //usage:        IF_FEATURE_UDHCPC_ARPING(
-//usage:     "\n        -a,--arping             Use arping to validate offered address"
+//usage:     "\n        -a[MSEC],--arping[=MSEC] Validate offered address with ARP ping"
 //usage:        )
 //usage:     "\n        -r,--request IP         Request this IP address"
 //usage:     "\n        -o,--no-default-options Don't request any options (unless -O is given)"
@@ -1211,7 +1211,7 @@ static void client_background(void)
 //usage:        )
 //usage:     "\n        -S              Log to syslog too"
 //usage:        IF_FEATURE_UDHCPC_ARPING(
-//usage:     "\n        -a              Use arping to validate offered address"
+//usage:     "\n        -a[MSEC]        Validate offered address with ARP ping"
 //usage:        )
 //usage:     "\n        -r IP           Request this IP address"
 //usage:     "\n        -o              Don't request any options (unless -O is given)"
@@ -1238,6 +1238,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 {
         uint8_t *message;
         const char *str_V, *str_h, *str_F, *str_r;
+        IF_FEATURE_UDHCPC_ARPING(const char *str_a = "2000";)
         IF_FEATURE_UDHCP_PORT(char *str_P;)
         void *clientid_mac_ptr;
         llist_t *list_O = NULL;
@@ -1252,6 +1253,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
         int timeout; /* must be signed */
         unsigned already_waited_sec;
         unsigned opt;
+        IF_FEATURE_UDHCPC_ARPING(unsigned arpping_ms;)
         int max_fd;
         int retval;
         fd_set rfds;
@@ -1269,7 +1271,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
         IF_LONG_OPTS(applet_long_options = udhcpc_longopts;)
         opt = getopt32(argv, "CV:H:h:F:i:np:qRr:s:T:t:SA:O:ox:fB"
                 USE_FOR_MMU("b")
-                IF_FEATURE_UDHCPC_ARPING("a")
+                IF_FEATURE_UDHCPC_ARPING("a::")
                 IF_FEATURE_UDHCP_PORT("P:")
                 "v"
                 , &str_V, &str_h, &str_h, &str_F
@@ -1278,6 +1280,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                 , &discover_timeout, &discover_retries, &tryagain_timeout /* T,t,A */
                 , &list_O
                 , &list_x
+                IF_FEATURE_UDHCPC_ARPING(, &str_a)
                 IF_FEATURE_UDHCP_PORT(, &str_P)
                 IF_UDHCP_VERBOSE(, &dhcp_verbose)
         );
@@ -1309,6 +1312,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                 SERVER_PORT = CLIENT_PORT - 1;
         }
 #endif
+        IF_FEATURE_UDHCPC_ARPING(arpping_ms = xatou(str_a);)
         while (list_O) {
                 char *optstr = llist_pop(&list_O);
                 unsigned n = bb_strtou(optstr, NULL, 0);
@@ -1726,7 +1730,8 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
                                                         NULL,
                                                         (uint32_t) 0,
                                                         client_config.client_mac,
-                                                        client_config.interface)
+                                                        client_config.interface,
+                                                        arpping_ms)
                                         ) {
                                                 bb_info_msg("Offered address is in use "
                                                         "(got ARP reply), declining");
diff --git a/networking/udhcp/dhcpd.c b/networking/udhcp/dhcpd.c
index a1a7f6b57..4b3ed240c 100644
--- a/networking/udhcp/dhcpd.c
+++ b/networking/udhcp/dhcpd.c
@@ -28,6 +28,7 @@
 //usage:     "\n        -f      Run in foreground"
 //usage:     "\n        -S      Log to syslog too"
 //usage:     "\n        -I ADDR Local address"
+//usage:     "\n        -a MSEC Timeout for ARP ping (default 2000)"
 //usage:        IF_FEATURE_UDHCP_PORT(
 //usage:     "\n        -P N    Use port N (default 67)"
 //usage:        )
@@ -148,7 +149,8 @@ static uint32_t select_lease_time(struct dhcp_packet *packet)
 static NOINLINE void send_offer(struct dhcp_packet *oldpacket,
                 uint32_t static_lease_nip,
                 struct dyn_lease *lease,
-                uint8_t *requested_ip_opt)
+                uint8_t *requested_ip_opt,
+                unsigned arpping_ms)
 {
         struct dhcp_packet packet;
         uint32_t lease_time_sec;
@@ -187,7 +189,7 @@ static NOINLINE void send_offer(struct dhcp_packet *oldpacket,
                 }
                 else {
                         /* Otherwise, find a free IP */
-                        packet.yiaddr = find_free_or_expired_nip(oldpacket->chaddr);
+                        packet.yiaddr = find_free_or_expired_nip(oldpacket->chaddr, arpping_ms);
                 }
 
                 if (!packet.yiaddr) {
@@ -304,6 +306,8 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
         unsigned opt;
         struct option_set *option;
         char *str_I = str_I;
+        const char *str_a = "2000";
+        unsigned arpping_ms;
         IF_FEATURE_UDHCP_PORT(char *str_P;)
 
 #if ENABLE_FEATURE_UDHCP_PORT
@@ -314,9 +318,10 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
 #if defined CONFIG_UDHCP_DEBUG && CONFIG_UDHCP_DEBUG >= 1
         opt_complementary = "vv";
 #endif
-        opt = getopt32(argv, "fSI:v"
+        opt = getopt32(argv, "fSI:va:"
                 IF_FEATURE_UDHCP_PORT("P:")
                 , &str_I
+                , &str_a
                 IF_FEATURE_UDHCP_PORT(, &str_P)
                 IF_UDHCP_VERBOSE(, &dhcp_verbose)
                 );
@@ -336,11 +341,13 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
                 free(lsa);
         }
 #if ENABLE_FEATURE_UDHCP_PORT
-        if (opt & 16) { /* -P */
+        if (opt & 32) { /* -P */
                 SERVER_PORT = xatou16(str_P);
                 CLIENT_PORT = SERVER_PORT + 1;
         }
 #endif
+        arpping_ms = xatou(str_a);
+
         /* Would rather not do read_config before daemonization -
          * otherwise NOMMU machines will parse config twice */
         read_config(argv[0] ? argv[0] : DHCPD_CONF_FILE);
@@ -498,7 +505,7 @@ int udhcpd_main(int argc UNUSED_PARAM, char **argv)
                 case DHCPDISCOVER:
                         log1("Received DISCOVER");
 
-                        send_offer(&packet, static_lease_nip, lease, requested_ip_opt);
+                        send_offer(&packet, static_lease_nip, lease, requested_ip_opt, arpping_ms);
                         break;
 
                 case DHCPREQUEST:
diff --git a/networking/udhcp/dhcpd.h b/networking/udhcp/dhcpd.h
index a77724f20..183e7e24c 100644
--- a/networking/udhcp/dhcpd.h
+++ b/networking/udhcp/dhcpd.h
@@ -100,7 +100,7 @@ struct dyn_lease *add_lease(
 int is_expired_lease(struct dyn_lease *lease) FAST_FUNC;
 struct dyn_lease *find_lease_by_mac(const uint8_t *mac) FAST_FUNC;
 struct dyn_lease *find_lease_by_nip(uint32_t nip) FAST_FUNC;
-uint32_t find_free_or_expired_nip(const uint8_t *safe_mac) FAST_FUNC;
+uint32_t find_free_or_expired_nip(const uint8_t *safe_mac, unsigned arpping_ms) FAST_FUNC;
 
 
 /* Config file parser will pass static lease info to this function
diff --git a/networking/udhcp/leases.c b/networking/udhcp/leases.c
index c5b60b108..745340ad3 100644
--- a/networking/udhcp/leases.c
+++ b/networking/udhcp/leases.c
@@ -112,7 +112,7 @@ struct dyn_lease* FAST_FUNC find_lease_by_nip(uint32_t nip)
 }
 
 /* Check if the IP is taken; if it is, add it to the lease table */
-static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac)
+static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac, unsigned arpping_ms)
 {
         struct in_addr temp;
         int r;
@@ -120,7 +120,8 @@ static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac)
         r = arpping(nip, safe_mac,
                         server_config.server_nip,
                         server_config.server_mac,
-                        server_config.interface);
+                        server_config.interface,
+                        arpping_ms);
         if (r)
                 return r;
 
@@ -132,7 +133,7 @@ static int nobody_responds_to_arp(uint32_t nip, const uint8_t *safe_mac)
 }
 
 /* Find a new usable (we think) address */
-uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac)
+uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac, unsigned arpping_ms)
 {
         uint32_t addr;
         struct dyn_lease *oldest_lease = NULL;
@@ -177,7 +178,7 @@ uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac)
                 lease = find_lease_by_nip(nip);
                 if (!lease) {
 //TODO: DHCP servers do not always sit on the same subnet as clients: should *ping*, not arp-ping!
-                        if (nobody_responds_to_arp(nip, safe_mac))
+                        if (nobody_responds_to_arp(nip, safe_mac, arpping_ms))
                                 return nip;
                 } else {
                         if (!oldest_lease || lease->expires < oldest_lease->expires)
@@ -194,7 +195,7 @@ uint32_t FAST_FUNC find_free_or_expired_nip(const uint8_t *safe_mac)
 
         if (oldest_lease
          && is_expired_lease(oldest_lease)
-         && nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac)
+         && nobody_responds_to_arp(oldest_lease->lease_nip, safe_mac, arpping_ms)
         ) {
                 return oldest_lease->lease_nip;
         }