Add --tftp-mtu option.

CHANGELOG

@@ -53,6 +53,10 @@ version 2.76
 
 	    Add --dhcp-ttl option.
 
+	    Add --tftp-mtu option. Thanks to Patrick McLean for the 
+	    initial patch.
+
+
 version 2.75
             Fix reversion on 2.74 which caused 100% CPU use when a 
 	    dhcp-script is configured. Thanks to Adrian Davey for

man/dnsmasq.8

@@ -1810,6 +1810,10 @@ require about (2*n) + 10 descriptors. If
 .B --tftp-port-range
 is given, that can affect the number of concurrent connections.
 .TP
+.B --tftp-mtu=<mtu size>
+Use size as the ceiling of the MTU supported by the intervening network when 
+negotiating TFTP blocksize, overriding the MTU setting of the local interface  if it is larger.
+.TP
 .B --tftp-no-blocksize
 Stop the TFTP server from negotiating the "blocksize" option with a
 client. Some buggy clients request this option but then behave badly

src/dnsmasq.h

@@ -975,7 +975,7 @@ extern struct daemon {
   struct dhcp_netid_list *dhcp_ignore, *dhcp_ignore_names, *dhcp_gen_names; 
   struct dhcp_netid_list *force_broadcast, *bootp_dynamic;
   struct hostsfile *dhcp_hosts_file, *dhcp_opts_file, *dynamic_dirs;
-  int dhcp_max, tftp_max;
+  int dhcp_max, tftp_max, tftp_mtu;
   int dhcp_server_port, dhcp_client_port;
   int start_tftp_port, end_tftp_port; 
   unsigned int min_leasetime;

src/option.c

@@ -158,7 +158,8 @@ struct myoption {
 #define LOPT_CPE_ID        346
 #define LOPT_SCRIPT_ARP    347
 #define LOPT_DHCPTTL       348
-
+#define LOPT_TFTP_MTU      349
+ 
 #ifdef HAVE_GETOPT_LONG
 static const struct option opts[] =  
 #else
@@ -244,6 +245,7 @@ static const struct myoption opts[] =
     { "tftp-unique-root", 0, 0, LOPT_APREF },
     { "tftp-root", 1, 0, LOPT_PREFIX },
     { "tftp-max", 1, 0, LOPT_TFTP_MAX },
+    { "tftp-mtu", 1, 0, LOPT_TFTP_MTU },
     { "tftp-lowercase", 0, 0, LOPT_TFTP_LC },
     { "ptr-record", 1, 0, LOPT_PTR },
     { "naptr-record", 1, 0, LOPT_NAPTR },
@@ -432,6 +434,7 @@ static struct {
   { LOPT_SECURE, OPT_TFTP_SECURE, NULL, gettext_noop("Allow access only to files owned by the user running dnsmasq."), NULL },
   { LOPT_TFTP_NO_FAIL, OPT_TFTP_NO_FAIL, NULL, gettext_noop("Do not terminate the service if TFTP directories are inaccessible."), NULL },
   { LOPT_TFTP_MAX, ARG_ONE, "<integer>", gettext_noop("Maximum number of conncurrent TFTP transfers (defaults to %s)."), "#" },
+  { LOPT_TFTP_MTU, ARG_ONE, "<integer>", gettext_noop("Maximum MTU to use for TFTP transfers."), NULL },
   { LOPT_NOBLOCK, OPT_TFTP_NOBLOCK, NULL, gettext_noop("Disable the TFTP blocksize extension."), NULL },
   { LOPT_TFTP_LC, OPT_TFTP_LC, NULL, gettext_noop("Convert TFTP filenames to lowercase"), NULL },
   { LOPT_TFTPPORTS, ARG_ONE, "<start>,<end>", gettext_noop("Ephemeral port range for use by TFTP transfers."), NULL },
@@ -2625,6 +2628,11 @@ static int one_opt(int option, char *arg, char *errstr, char *gen_err, int comma
 	ret_err(gen_err);
       break;  
 
+    case LOPT_TFTP_MTU:  /*  --tftp-mtu */
+      if (!atoi_check(arg, &daemon->tftp_mtu))
+	ret_err(gen_err);
+      break;
+
     case LOPT_PREFIX: /* --tftp-prefix */
       comma = split(arg);
       if (comma)

src/tftp.c

@@ -103,8 +103,10 @@ void tftp_request(struct listener *listen, time_t now)
       if (listen->iface)
 	{
 	  addr = listen->iface->addr;
-	  mtu = listen->iface->mtu;
 	  name = listen->iface->name;
+	  mtu = listen->iface->mtu;
+	  if (daemon->tftp_mtu != 0 && daemon->tftp_mtu < mtu)
+	    mtu = daemon->tftp_mtu;
 	}
       else
 	{
@@ -234,9 +236,17 @@ void tftp_request(struct listener *listen, time_t now)
 
       strncpy(ifr.ifr_name, name, IF_NAMESIZE);
       if (ioctl(listen->tftpfd, SIOCGIFMTU, &ifr) != -1)
-	mtu = ifr.ifr_mtu;      
+	{
+	  mtu = ifr.ifr_mtu;  
+	  if (daemon->tftp_mtu != 0 && daemon->tftp_mtu < mtu)
+	    mtu = daemon->tftp_mtu;    
+	}
     }
 
+  /* Failed to get interface mtu - can use configured value. */
+  if (mtu == 0)
+    mtu = daemon->tftp_mtu;
+
   if (name)
     {
       /* check for per-interface prefix */