T: add a 'multi' tracer

This tracer allows the connection of several tracers to one tracee.

To use the multi tracer:
- run the tracee as usual, eg. ./lte-softmodem -O xxxx.conf --T_stdout 0
- run the multi tracer: ./multi -d ../T_messages.txt
- connect other tracers to the multi tracer:
   - ./enb -d ../T_messages.txt -p 2022
   - ./textlog -d ../T_messages.txt -p 2022
   - etc.

By default the multi tracer connects to the tracee to the port 2021,
as for any other tracer.

Then it accepts connections from other tracers on the port 2022.

This can be changed with parameters on the command line.

The tracee and the other tracers can be stopped/started at any time.

common/utils/T/tracer/utils.c

@@ -79,6 +79,36 @@ list *list_append(list *l, void *data)
 /* socket                                                                   */
 /****************************************************************************/
 
+int create_listen_socket(char *addr, int port)
+{
+  struct sockaddr_in a;
+  int s;
+  int v;
+
+  s = socket(AF_INET, SOCK_STREAM, 0);
+  if (s == -1) { perror("socket"); exit(1); }
+  v = 1;
+  if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &v, sizeof(int)))
+    { perror("setsockopt"); exit(1); }
+
+  a.sin_family = AF_INET;
+  a.sin_port = htons(port);
+  a.sin_addr.s_addr = inet_addr(addr);
+
+  if (bind(s, (struct sockaddr *)&a, sizeof(a))) { perror("bind"); exit(1); }
+  if (listen(s, 5)) { perror("listen"); exit(1); }
+
+  return s;
+}
+
+int socket_accept(int s)
+{
+  struct sockaddr_in a;
+  socklen_t alen;
+  alen = sizeof(a);
+  return accept(s, (struct sockaddr *)&a, &alen);
+}
+
 int socket_send(int socket, void *buffer, int size)
 {
   char *x = buffer;
@@ -94,26 +124,13 @@ int socket_send(int socket, void *buffer, int size)
 
 int get_connection(char *addr, int port)
 {
-  struct sockaddr_in a;
-  socklen_t alen;
   int s, t;
 
   printf("waiting for connection on %s:%d\n", addr, port);
 
-  s = socket(AF_INET, SOCK_STREAM, 0);
-  if (s == -1) { perror("socket"); exit(1); }
-  t = 1;
-  if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR, &t, sizeof(int)))
-    { perror("setsockopt"); exit(1); }
+  s = create_listen_socket(addr, port);
 
-  a.sin_family = AF_INET;
-  a.sin_port = htons(port);
-  a.sin_addr.s_addr = inet_addr(addr);
-
-  if (bind(s, (struct sockaddr *)&a, sizeof(a))) { perror("bind"); exit(1); }
-  if (listen(s, 5)) { perror("bind"); exit(1); }
-  alen = sizeof(a);
-  t = accept(s, (struct sockaddr *)&a, &alen);
+  t = socket_accept(s);
   if (t == -1) { perror("accept"); exit(1); }
   close(s);
 
@@ -137,14 +154,11 @@ int fullread(int fd, void *_buf, int count)
   return ret;
 }
 
-int connect_to(char *addr, int port)
+int try_connect_to(char *addr, int port)
 {
   int s;
   struct sockaddr_in a;
 
-  printf("connecting to %s:%d\n", addr, port);
-
-again:
   s = socket(AF_INET, SOCK_STREAM, 0);
   if (s == -1) { perror("socket"); exit(1); }
 
@@ -155,6 +169,21 @@ again:
   if (connect(s, (struct sockaddr *)&a, sizeof(a)) == -1) {
     perror("connect");
     close(s);
+    return -1;
+  }
+
+  return s;
+}
+
+int connect_to(char *addr, int port)
+{
+  int s;
+
+  printf("connecting to %s:%d\n", addr, port);
+
+again:
+  s = try_connect_to(addr, port);
+  if (s == -1) {
     printf("trying again in 1s\n");
     sleep(1);
     goto again;