reduce code complexity

Signed-off-by: Mattias Andrée <maandree@operamail.com>

4 files changed, 391 insertions, 468 deletions

diff --git a/src/mds-server/mds-server.c b/src/mds-server/mds-server.c
index 5b81222..8bb7b83 100644
--- a/src/mds-server/mds-server.c
+++ b/src/mds-server/mds-server.c
@@ -137,7 +137,6 @@ static pthread_cond_t modify_cond;
 static hash_table_t modify_map;
 
 
-
 /**
  * Entry point of the server
  * 
@@ -160,24 +159,21 @@ int main(int argc_, char** argv_)
 #endif
   
   
+#define exit_if(CONDITION, INSTRUCTION)  if (CONDITION) { INSTRUCTION return 1; }
+  
+  
   argc = argc_;
   argv = argv_;
   
   
   /* Drop privileges like it's hot. */
   if (drop_privileges())
-    {
-      perror(*argv);
-      return 1;
-    }
+    goto pfail;
   
   
   /* Sanity check the number of command line arguments. */
-  if (argc > ARGC_LIMIT + LIBEXEC_ARGC_EXTRA_LIMIT)
-    {
-      eprint("that number of arguments is ridiculous, I will not allow it.");
-      return 1;
-    }
+  exit_if (argc > ARGC_LIMIT + LIBEXEC_ARGC_EXTRA_LIMIT,
+	   eprint("that number of arguments is ridiculous, I will not allow it."););
   
   
   /* Parse command line arguments. */
@@ -187,26 +183,18 @@ int main(int argc_, char** argv_)
       int v;
       if ((v = strequals(arg, "--initial-spawn")) || /* Initial spawn? */
 	  strequals(arg, "--respawn"))               /* Respawning after crash? */
-	if (is_respawn == v)
-	  {
-	    eprintf("conflicting arguments %s and %s cannot be combined.",
-		    "--initial-spawn", "--respawn");
-	    return 1;
-	  }
-	else
+	{
+	  exit_if (is_respawn == v,
+		   eprintf("conflicting arguments %s and %s cannot be combined.",
+			   "--initial-spawn", "--respawn"););
 	  is_respawn = !v;
+	}
       else if (startswith(arg, "--socket-fd=")) /* Socket file descriptor. */
 	{
-	  if (socket_fd != -1)
-	    {
-	      eprintf("duplicate declaration of %s.", "--socket-fd");
-	      return 1;
-	    }
-	  if (strict_atoi(arg += strlen("--socket-fd="), &socket_fd, 0, INT_MAX) < 0)
-	    {
-	      eprintf("invalid value for %s: %s.", "--socket-fd", arg);
-	      return 1;
-	    }
+	  exit_if (socket_fd != -1,
+		   eprintf("duplicate declaration of %s.", "--socket-fd"););
+	  exit_if (strict_atoi(arg += strlen("--socket-fd="), &socket_fd, 0, INT_MAX) < 0,
+		   eprintf("invalid value for %s: %s.", "--socket-fd", arg););
 	}
       else if (strequals(arg, "--re-exec")) /* Re-exec state-marshal. */
 	reexec = 1;
@@ -223,17 +211,14 @@ int main(int argc_, char** argv_)
   
   
   /* Check that manditory arguments have been specified. */
-  if (is_respawn < 0)
-    {
-      eprintf("missing state argument, require either %s or %s.",
-	      "--initial-spawn", "--respawn");
-      return 1;
-    }
-  if (socket_fd < 0)
-    {
-      eprint("missing socket file descriptor argument.");
-      return 1;
-    }
+  exit_if (is_respawn < 0,
+	   eprintf("missing state argument, require either %s or %s.",
+		   "--initial-spawn", "--respawn"););
+  exit_if (socket_fd < 0,
+	   eprint("missing socket file descriptor argument."););
+  
+  
+#undef exit_if
   
   
   /* Run mdsinitrc. */
@@ -241,16 +226,13 @@ int main(int argc_, char** argv_)
     {
       pid_t pid = fork();
       if (pid == (pid_t)-1)
-	{
-	  perror(*argv);
-	  return 1;
-	}
+	goto pfail;
       if (pid == 0) /* Child process exec:s, the parent continues without waiting for it. */
 	{
 	  /* Close all files except stdin, stdout and stderr. */
 	  close_files((fd > 2) || (fd == socket_fd));
 	  
-	  /* Run initrc */
+	  /* Run mdsinitrc. */
 	  run_initrc(unparsed_args);
 	  return 1;
 	}
@@ -265,78 +247,36 @@ int main(int argc_, char** argv_)
   if (I >= 5)  pthread_cond_destroy(&modify_cond);         \
   if (I >= 6)  hash_table_destroy(&modify_map, NULL, NULL)
   
+#define __error(I)  perror(*argv); __free(I); return 1
+  
   
   /* Create list and table of clients. */
   if (reexec == 0)
     {
-      if (fd_table_create(&client_map))
-	{
-	  perror(*argv);
-	  __free(0);
-	  return 1;
-	}
-      if (linked_list_create(&client_list, 32))
-	{
-	  perror(*argv);
-	  __free(1);
-	  return 1;
-	}
+      if (fd_table_create(&client_map))          { __error(0); }
+      if (linked_list_create(&client_list, 32))  { __error(1); }
     }
   
   
   /* Store the current thread so it can be killed from elsewhere. */
   master_thread = pthread_self();
   
-  
   /* Make the server update without all slaves dying on SIGUSR1. */
-  if (xsigaction(SIGUSR1, sigusr1_trap) < 0)
-    {
-      perror(*argv);
-      __free(1);
-      return 1;
-    }
+  if (xsigaction(SIGUSR1, sigusr1_trap) < 0)              { __error(1); }
   
   /* Implement clean exit on SIGTERM. */
-  if (xsigaction(SIGTERM, sigterm_trap) < 0)
-    {
-      perror(*argv);
-      __free(1);
-      return 1;
-    }
+  if (xsigaction(SIGTERM, sigterm_trap) < 0)              { __error(1); }
   
   /* Create mutex and condition for slave counter. */
-  if ((errno = pthread_mutex_init(&slave_mutex, NULL)) != 0)
-    {
-      perror(*argv);
-      __free(1);
-      return 1;
-    }
-  if ((errno = pthread_cond_init(&slave_cond, NULL)) != 0)
-    {
-      perror(*argv);
-      __free(2);
-      return 1;
-    }
+  if ((errno = pthread_mutex_init(&slave_mutex, NULL)))   { __error(1); }
+  if ((errno = pthread_cond_init(&slave_cond, NULL)))     { __error(2); }
   
   /* Create mutex, condition and map for message modification. */
-  if ((errno = pthread_mutex_init(&modify_mutex, NULL)) != 0)
-    {
-      perror(*argv);
-      __free(3);
-      return 1;
-    }
-  if ((errno = pthread_cond_init(&modify_cond, NULL)) != 0)
-    {
-      perror(*argv);
-      __free(4);
-      return 1;
-    }
-  if (hash_table_create(&modify_map))
-    {
-      perror(*argv);
-      __free(5);
-      return 1;
-    }
+  if ((errno = pthread_mutex_init(&modify_mutex, NULL)))  { __error(3); }
+  if ((errno = pthread_cond_init(&modify_cond, NULL)))    { __error(4); }
+  if (hash_table_create(&modify_map))                     { __error(5); }
+
+#undef __error
   
   
   /* Unmarshal the state of the server. */
@@ -400,15 +340,7 @@ int main(int argc_, char** argv_)
       with_mutex(slave_mutex, running_slaves++;);
       
       /* Start slave thread. */
-      errno = pthread_create(&slave_thread, NULL, slave_loop, (void*)(intptr_t)client_fd);
-      if (errno)
-	{
-	  perror(*argv);
-	  with_mutex(slave_mutex, running_slaves--;);
-	}
-      errno = pthread_detach(slave_thread);
-	if (errno)
-	  perror(*argv);
+      create_slave(&slave_thread, client_fd);
     }
   
  terminate:
@@ -424,10 +356,10 @@ int main(int argc_, char** argv_)
   /* Release resources. */
   __free(9999);
   
-#undef __free
-  
   return 0;
   
+#undef __free
+  
   
  reexec:
   {
@@ -452,10 +384,7 @@ int main(int argc_, char** argv_)
     xsnprintf(shm_path, SHM_PATH_PATTERN, (unsigned long int)pid);
     reexec_fd = shm_open(shm_path, O_RDWR | O_CREAT | O_EXCL, S_IRWXU);
     if (reexec_fd < 0)
-      {
-	perror(*argv);
-	return 1;
-      }
+      goto pfail;
     if (marshal_server(reexec_fd) < 0)
       goto reexec_fail;
     close(reexec_fd);
@@ -482,6 +411,10 @@ int main(int argc_, char** argv_)
        be respawn if the re-exec fails. */
     return 1;
   }
+  
+ pfail:
+  perror(*argv);
+  return 1;
 }
 
 
@@ -507,10 +440,7 @@ void* slave_loop(void* data)
     {
       /* Create information table. */
       if (xmalloc(information, 1, client_t))
-	{
-	  perror(*argv);
-	  goto fail;
-	}
+	goto pfail;
       
       /* NULL-out pointers and initialisation markers. */
       information->interception_conditions = NULL;
@@ -550,10 +480,7 @@ void* slave_loop(void* data)
       information->send_pending_size = 0;
       information->multicasts_count = 0;
       if (mds_message_initialise(&(information->message)))
-	{
-	  perror(*argv);
-	  goto fail;
-	}
+        goto pfail;
     }
   
   
@@ -561,129 +488,102 @@ void* slave_loop(void* data)
   information->thread = pthread_self();
   /* Create mutex to make sure two thread to not try to send
      messages concurrently, and other slave local actions. */
-  if ((errno = pthread_mutex_init(&(information->mutex), NULL)) != 0)
-    {
-      perror(*argv);
-      goto fail;
-    }
+  if ((errno = pthread_mutex_init(&(information->mutex), NULL)))         goto pfail;
   information->mutex_created = 1;
   
   /* Create mutex and codition for multicast interception replies. */
-  if ((errno = pthread_mutex_init(&(information->modify_mutex), NULL)) != 0)
-    {
-      perror(*argv);
-      goto fail;
-    }
+  if ((errno = pthread_mutex_init(&(information->modify_mutex), NULL)))  goto pfail;
   information->modify_mutex_created = 1;
-  if ((errno = pthread_cond_init(&(information->modify_cond), NULL)) != 0)
-    {
-      perror(*argv);
-      goto fail;
-    }
+  if ((errno = pthread_cond_init(&(information->modify_cond), NULL)))    goto pfail;
   information->modify_cond_created = 1;
   
   
   /* Make the server update without all slaves dying on SIGUSR1. */
-  if (xsigaction(SIGUSR1, sigusr1_trap) < 0)
-    {
-      perror(*argv);
-      goto fail;
-    }
+  if (xsigaction(SIGUSR1, sigusr1_trap) < 0)  goto pfail;
   
   /* Implement clean exit on SIGTERM. */
-  if (xsigaction(SIGTERM, sigterm_trap) < 0)
-    {
-      perror(*argv);
-      goto fail;
-    }
+  if (xsigaction(SIGTERM, sigterm_trap) < 0)  goto pfail;
   
   
   /* Fetch messages from the slave. */
-  if (information->open)
-    while (terminating == 0)
-      {
-	/* Send queued multicast messages. */
-	if (information->multicasts_count > 0)
+  while ((terminating == 0) && (information->open == 0))
+    {
+      /* Send queued multicast messages. */
+      if (information->multicasts_count > 0)
+	{
+	  multicast_t multicast;
+	  with_mutex(information->mutex,
+		     if (information->multicasts_count > 0)
+		       {
+			 size_t c = (information->multicasts_count -= 1) * sizeof(multicast_t);
+			 multicast = information->multicasts[0];
+			 memmove(information->multicasts, information->multicasts + 1, c);
+			 if (c == 0)
+			   {
+			     free(information->multicasts);
+			     information->multicasts = NULL;
+			   }
+		       }
+		     );
+	  multicast_message(&multicast);
+	  multicast_destroy(&multicast);
+	}
+      
+      /* Send queued messages. */
+      if (information->send_pending_size > 0)
+	{
+	  char* sendbuf = information->send_pending;
+	  char* sendbuf_ = sendbuf;
+	  size_t sent;
+	  n = information->send_pending_size;
+	  information->send_pending_size = 0;
+	  information->send_pending = NULL;
+	  with_mutex(information->mutex,
+		     while (n > 0)
+		       {
+			 sent = send_message(information->socket_fd, sendbuf_, n);
+			 if ((sent < n) && (errno != EINTR)) /* Ignore EINTR */
+			   {
+			     perror(*argv);
+			     break;
+			   }
+			 n -= sent;
+			 sendbuf_ += sent / sizeof(char);
+		       }
+		     free(sendbuf);
+		     );
+	}
+      
+      /* Fetch message. */
+      r = mds_message_read(&(information->message), socket_fd);
+      if (r == 0)
+	{
+	  if (message_received(information) == 1)
+	    goto terminate;
+	}
+      else
+	if (r == -2)
 	  {
-	    multicast_t multicast;
-	    with_mutex(information->mutex,
-		       if (information->multicasts_count > 0)
-			 {
-			   size_t c = information->multicasts_count -= 1;
-			   c *= sizeof(multicast_t);
-			   multicast = information->multicasts[0];
-			   memmove(information->multicasts, information->multicasts + 1, c);
-			   if (c == 0)
-			     {
-			       free(information->multicasts);
-			       information->multicasts = NULL;
-			     }
-			 }
-		       );
-	    multicast_message(&multicast);
-	    multicast_destroy(&multicast);
+	    eprint("corrupt message received.");
+	    goto fail;
 	  }
-	
-	/* Send queued messages. */
-	if (information->send_pending_size > 0)
+	else if (errno == ECONNRESET)
 	  {
-	    char* sendbuf = information->send_pending;
-	    char* sendbuf_ = sendbuf;
-	    size_t sent;
-	    n = information->send_pending_size;
-	    information->send_pending_size = 0;
-	    information->send_pending = NULL;
-	    with_mutex(information->mutex,
-		       while (n > 0)
-			 {
-			   sent = send_message(information->socket_fd, sendbuf_, n);
-			   if ((sent < n) && (errno != EINTR)) /* Ignore EINTR */
-			     {
-			       perror(*argv);
-			       break;
-			     }
-			   n -= sent;
-			   sendbuf_ += sent / sizeof(char);
-			 }
-		       free(sendbuf);
-		       );
+	    r = mds_message_read(&(information->message), socket_fd);
+	    if ((r == 0) && message_received(information))
+	      goto terminate;
+	    information->open = 0;
+	    /* Connection closed. */
 	  }
-	
-	/* Fetch message. */
-	r = mds_message_read(&(information->message), socket_fd);
-	if (r == 0)
+	else if (errno == EINTR)
 	  {
-	    if (message_received(information) == 1)
+	    /* Stop the thread if we are re-exec:ing the server. */
+	    if (terminating)
 	      goto terminate;
 	  }
 	else
-	  if (r == -2)
-	    {
-	      eprint("corrupt message received.");
-	      goto fail;
-	    }
-	  else if (errno == ECONNRESET)
-	    {
-	      r = mds_message_read(&(information->message), socket_fd);
-	      if (r == 0)
-		if (message_received(information))
-		  goto terminate;
-	      information->open = 0;
-	      /* Connection closed. */
-	      break;
-	    }
-	  else if (errno == EINTR)
-	    {
-	      /* Stop the thread if we are re-exec:ing the server. */
-	      if (terminating)
-		goto terminate;
-	    }
-	  else
-	    {
-	      perror(*argv);
-	      goto fail;
-	    }
-      }
+	  goto pfail;
+    }
   /* Stop the thread if we are re-exec:ing the server. */
   if (terminating)
     goto terminate;
@@ -725,6 +625,11 @@ void* slave_loop(void* data)
   return NULL;
   
   
+ pfail:
+  perror(*argv);
+  goto fail;
+  
+  
  reexec:
   /* Tell the master thread that the slave has closed,
      this is done because re-exec causes a race-condition
@@ -1037,46 +942,46 @@ void add_intercept_condition(client_t* client, char* condition, int64_t priority
      with for optimisation. */
   for (i = 0; i < n; i++)
     {
-      if (conds[i].header_hash == hash)
-	if (strequals(conds[i].condition, condition))
-	  {
-	    if (stop)
-	      {
-		/* Remove the condition from the list. */
-		memmove(conds + i, conds + i + 1, --n - i);
-		client->interception_conditions_count--;
-		/* Shrink the list. */
-		if (n == 0)
-		  {
-		    free(conds);
-		    client->interception_conditions = NULL;
-		  }
+      if ((conds[i].header_hash == hash) && strequals(conds[i].condition, condition))
+	{
+	  if (stop)
+	    {
+	      /* Remove the condition from the list. */
+	      memmove(conds + i, conds + i + 1, --n - i);
+	      client->interception_conditions_count--;
+	      /* Shrink the list. */
+	      if (n == 0)
+		{
+		  free(conds);
+		  client->interception_conditions = NULL;
+		}
+	      else
+		if ((conds = realloc(conds, n * sizeof(interception_condition_t))) == NULL)
+		  perror(*argv);
 		else
-		  if ((conds = realloc(conds, n * sizeof(interception_condition_t))) == NULL)
-		    perror(*argv);
-		  else
-		    client->interception_conditions = conds;
-	      }
-	    else
-	      {
-		/* Update parameters. */
-		conds[i].priority = priority;
-		conds[i].modifying = modifying;
-		if (modifying && (nonmodifying >= 0))
-		  {
-		    /* Optimisation: put conditions that are modifying
-		       at the beginning. When a client is intercepting
-		       we most know if any satisfying condition is
-		       modifying. With this optimisation the first
-		       satisfying condition will tell us if there is
-		       any satisfying condition that is modifying. */
-		    interception_condition_t temp = conds[nonmodifying];
-		    conds[nonmodifying] = conds[i];
-		    conds[i] = temp;
-		  }
-	      }
-	    return;
-	  }
+		  client->interception_conditions = conds;
+	    }
+	  else
+	    {
+	      /* Update parameters. */
+	      conds[i].priority = priority;
+	      conds[i].modifying = modifying;
+	      
+	      if (modifying && (nonmodifying >= 0))
+		{
+		  /* Optimisation: put conditions that are modifying
+		     at the beginning. When a client is intercepting
+		     we most know if any satisfying condition is
+		     modifying. With this optimisation the first
+		     satisfying condition will tell us if there is
+		     any satisfying condition that is modifying. */
+		  interception_condition_t temp = conds[nonmodifying];
+		  conds[nonmodifying] = conds[i];
+		  conds[i] = temp;
+		}
+	    }
+	  return;
+	}
       /* Look for the first non-modifying, this is a part of the
          optimisation where we put all modifying conditions at the
 	 beginning. */
@@ -1411,79 +1316,79 @@ void multicast_message(multicast_t* multicast)
 	    continue;
 	}
       
-      /* Wait for a reply and act upon it. */
-      if ((n == 0) && client_.modifying)
+      /* Do not wait for a reply if it is non-modifying. */
+      if (client_.modifying)
 	{
-	  /* pthread_cond_timedwait is required to handle re-exec because
-	     pthread_cond_timedwait and pthread_cond_wait ignore interruptions via signals. */
-	  struct timespec timeout =
-	    {
-	      .tv_sec = 1,
-	      .tv_nsec = 0
-	    };
-	  int modifying = 0;
-	  char* old_buf;
-	  size_t i;
-	  mds_message_t* mod;
-	  
-	  /* Wait for a reply. */
-	  with_mutex(modify_mutex,
-		     if (client->modify_message == NULL)
-		       {
-			 if (hash_table_contains_key(&modify_map, (size_t)modify_id) == 0)
-			   {
-			     hash_table_put(&modify_map, (size_t)modify_id, (size_t)(void*)client);
-			     pthread_cond_signal(&slave_cond);
-			   }
-		       }
-		     );
-	  with_mutex(client->modify_mutex,
-		     if (client->modify_message == NULL)
-		       {
-			 for (;;)
-			   {
-			     pthread_cond_timedwait(&slave_cond, &slave_mutex, &timeout);
-			     if ((client->modify_message != NULL) && terminating)
-			       break;
-			   }
-			 if (terminating == 0)
-			   hash_table_remove(&modify_map, (size_t)modify_id);
-		       }
-		     );
-	  if (terminating)
-	    return;
-	  
-	  /* Act upon the reply. */
-	  if (client->modify_message != NULL)
-	    {
-	      mod = client->modify_message;
-	      for (i = 0; i < mod->header_count; i++)
-		if (!strcmp(mod->headers[i], "Modify: yes"))
-		  {
-		    modifying = 1;
-		    break;
-		  }
-	      if (modifying)
-		{
-		  old_buf = multicast->message;
-		  n = mod->payload_size;
-		  multicast->message = realloc(old_buf, (multicast->message_prefix + n) * sizeof(char));
-		  if (multicast->message == NULL)
-		    {
-		      perror(*argv);
-		      multicast->message = old_buf;
-		    }
-		  else
-		    memcpy(multicast->message + multicast->message_prefix, mod->payload, n);
-		}
-	      
-	      /* Free the reply. */
-	      mds_message_destroy(client->modify_message);
-	    }
+	  /* Reset how much of the message has been sent before we continue with next recipient. */
+	  multicast->message_ptr = 0;
+	  continue;
 	}
       
-      /* Reset how much of the message has been sent before we continue with next recipient. */
-      multicast->message_ptr = 0;
+      /* Wait for a reply and act upon it. */
+      {
+	/* pthread_cond_timedwait is required to handle re-exec because
+	   pthread_cond_timedwait and pthread_cond_wait ignore interruptions via signals. */
+	struct timespec timeout =
+	  {
+	    .tv_sec = 1,
+	    .tv_nsec = 0
+	  };
+	int modifying = 0;
+	char* old_buf;
+	size_t i;
+	mds_message_t* mod;
+	
+	/* Wait for a reply. */
+	with_mutex(modify_mutex,
+		   if (client->modify_message == NULL)
+		     {
+		       if (hash_table_contains_key(&modify_map, (size_t)modify_id) == 0)
+			 {
+			   hash_table_put(&modify_map, (size_t)modify_id, (size_t)(void*)client);
+			   pthread_cond_signal(&slave_cond);
+			 }
+		     }
+		   );
+	with_mutex(client->modify_mutex,
+		   if (client->modify_message == NULL)
+		     {
+		       while ((client->modify_message == NULL) && (terminating == 0))
+			 pthread_cond_timedwait(&slave_cond, &slave_mutex, &timeout);
+		       if (terminating == 0)
+			 hash_table_remove(&modify_map, (size_t)modify_id);
+		     }
+		   );
+	if (terminating)
+	  return;
+	
+	/* Act upon the reply. */
+	mod = client->modify_message;
+	for (i = 0; i < mod->header_count; i++)
+	  if (!strcmp(mod->headers[i], "Modify: yes"))
+	    {
+	      modifying = 1;
+	      break;
+	    }
+	if (modifying)
+	  {
+	    old_buf = multicast->message;
+	    n = mod->payload_size;
+	    multicast->message = realloc(old_buf, (multicast->message_prefix + n) * sizeof(char));
+	    if (multicast->message == NULL)
+	      {
+		perror(*argv);
+		multicast->message = old_buf;
+	      }
+	    else
+	      memcpy(multicast->message + multicast->message_prefix, mod->payload, n);
+	  }
+	
+	/* Free the reply. */
+	mds_message_destroy(client->modify_message);
+	
+	/* Reset how much of the message has been sent before we continue with next recipient. */
+	multicast->message_ptr = 0;
+      }
     }
 }
 
@@ -1809,18 +1714,12 @@ int unmarshal_server(int fd)
   
   /* Unmarshal the client list. */
   if (linked_list_unmarshal(&client_list, state_buf_))
-    {
-      perror(*argv);
-      abort(); /* Critical. */
-    }
+    goto critical_fail;
   state_buf_ += list_size / sizeof(char);
   
   /* Unmarshal the client map. */
   if (fd_table_unmarshal(&client_map, state_buf_, unmarshal_remapper))
-    {
-      perror(*argv);
-      abort(); /* Critical. */
-    }
+    goto critical_fail;
   
   /* Release the raw data. */
   free(state_buf);
@@ -1851,15 +1750,7 @@ int unmarshal_server(int fd)
 	  with_mutex(slave_mutex, running_slaves++;);
 	  
 	  /* Start slave thread. */
-	  errno = pthread_create(&slave_thread, NULL, slave_loop, (void*)(intptr_t)socket_fd);
-	  if (errno)
-	    {
-	      perror(*argv);
-	      with_mutex(slave_mutex, running_slaves--;);
-	    }
-	  errno = pthread_detach(slave_thread);
-	  if (errno)
-	    perror(*argv);
+	  create_slave(&slave_thread, socket_fd);
 	}
     }
   
@@ -1867,5 +1758,33 @@ int unmarshal_server(int fd)
   hash_table_destroy(&unmarshal_remap_map, NULL, NULL);
   
   return -with_error;
+
+ critical_fail:
+  perror(*argv);
+  abort();
+}
+
+
+/**
+ * Create, start and detache a slave thread
+ * 
+ * @param   thread     The address at where to store the thread
+ * @param   socket_fd  The file descriptor of the slave's socket
+ * @return             Zero on success, -1 on error, error message will have been printed
+ */
+int create_slave(pthread_t* thread_slot, int socket_fd)
+{
+  if ((errno = pthread_create(thread_slot, NULL, slave_loop, (void*)(intptr_t)socket_fd)))
+    {
+      perror(*argv);
+      with_mutex(slave_mutex, running_slaves--;);
+      return -1;
+    }
+  if ((errno = pthread_detach(*thread_slot)))
+    {
+      perror(*argv);
+      return -1;
+    }
+  return 0;
 }
 
diff --git a/src/mds-server/mds-server.h b/src/mds-server/mds-server.h
index 43662d7..08f7fd4 100644
--- a/src/mds-server/mds-server.h
+++ b/src/mds-server/mds-server.h
@@ -116,6 +116,15 @@ int marshal_server(int fd);
  */
 int unmarshal_server(int fd);
 
+/**
+ * Create, start and detache a slave thread
+ * 
+ * @param   thread     The address at where to store the thread
+ * @param   socket_fd  The file descriptor of the slave's socket
+ * @return             Zero on success, -1 on error, error message will have been printed
+ */
+int create_slave(pthread_t* thread_slot, int socket_fd);
+
 
 #endif
 
diff --git a/src/mds.c b/src/mds.c
index 16d6275..c466846 100644
--- a/src/mds.c
+++ b/src/mds.c
@@ -69,9 +69,12 @@ int main(int argc_, char** argv_)
   char pathname[PATH_MAX];
   char piddata[64];
   unsigned int display;
-  FILE *f;
+  FILE* f;
   int rc;
-  int j;
+  int j, r;
+  
+  
+#define exit_if(CONDITION, INSTRUCTION)  if (CONDITION) { INSTRUCTION return 1; }
   
   
   argc = argc_;
@@ -79,11 +82,8 @@ int main(int argc_, char** argv_)
   
   
   /* Sanity check the number of command line arguments. */
-  if (argc > ARGC_LIMIT)
-    {
-      eprint("that number of arguments is ridiculous, I will not allow it.");
-      return 1;
-    }
+  exit_if (argc > ARGC_LIMIT,
+	   eprint("that number of arguments is ridiculous, I will not allow it."););
   
   /* Parse command line arguments. */
   for (j = 1; j < argc; j++)
@@ -91,29 +91,20 @@ int main(int argc_, char** argv_)
       char* arg = argv[j];
       if (startswith(arg, "--master-server=")) /* Master server. */
 	{
-	  if (got_master_server)
-	    {
-	      eprintf("duplicate declaration of %s.", "--master-server");
-	      return 1;
-	    }
+	  exit_if (got_master_server,
+		   eprintf("duplicate declaration of %s.", "--master-server"););
 	  got_master_server = 1;
 	  master_server = arg + strlen("--master-server=");
 	}
     }
   
   /* Stymied if the effective user is not root. */
-  if (geteuid() != ROOT_USER_UID)
-    {
-      eprint("the effective user is not root, cannot continue.");
-      return 1;
-    }
+  exit_if (geteuid() != ROOT_USER_UID,
+	   eprint("the effective user is not root, cannot continue."););
   
   /* Set up to ignore SIGUSR1, used in mds for re-exec, but we cannot re-exec. */
   if (xsigaction(SIGUSR1, SIG_IGN) < 0)
-    {
-      perror(*argv);
-      eprint("while ignoring the SIGUSR1 signal.");
-    }
+    perror(*argv);
   
   /* Create directory for socket files, PID files and such. */
   if (create_directory_root(MDS_RUNTIME_ROOT_DIRECTORY))
@@ -127,88 +118,42 @@ int main(int argc_, char** argv_)
       fd = open(pathname, O_CREAT | O_EXCL);
       if (fd == -1)
 	{
-	  /* Reuse display index not no longer used. */
-	  size_t read_len;
+	  /* Reuse display index if no longer used. */
 	  f = fopen(pathname, "r");
 	  if (f == NULL) /* Race, or error? */
 	    {
 	      perror(*argv);
-	      eprintf("while opening the file: %s", pathname);
 	      continue;
 	    }
-	  read_len = fread(piddata, 1, sizeof(piddata) / sizeof(char), f);
-	  if (ferror(f)) /* Failed to read. */
-	    {
-	      perror(*argv);
-	      eprintf("while reading the file: %s", pathname);
-	    }
-	  else if (feof(f) == 0) /* Did not read everything. */
-	    eprint("the content of a PID file is longer than expected.");
-	  else
-	    {
-	      pid_t pid = 0;
-	      size_t i, n = read_len - 1;
-	      for (i = 0; i < n; i++)
-		{
-		  char c = piddata[i];
-		  if (('0' <= c) && (c <= '9'))
-		    pid = pid * 10 + (c & 15);
-		  else
-		    {
-		      eprint("the content of a PID file is invalid.");
-		      goto bad;
-		    }
-		}
-	      if (piddata[n] != '\n')
-		{
-		  eprint("the content of a PID file is invalid.");
-		  goto bad;
-		}
-	      if (kill(pid, 0) < 0) /* Check if the PID is still allocated to any process. */
-		if (errno == ESRCH) /* PID is not used. */
-		  {
-		    fclose(f);
-		    close(fd);
-		    break;
-		  }
-	    }
-	bad:
+	  r = is_pid_file_reusable(f);
 	  fclose(f);
-	  continue;
+	  if (r == 0)
+	    continue;
 	}
       close(fd);
       break;
     }
-  if (display == DISPLAY_MAX)
-    {
-      eprint("sorry, too many displays on the system.");
-      return 1;
-      /* Yes, the directory could have been removed, but it probably was not. */
-    }
+  exit_if (display == DISPLAY_MAX,
+	   eprint("sorry, too many displays on the system."););
+           /* Yes, the directory could have been removed, but it probably was not. */
+  
+#undef exit_if
   
   /* Create PID file. */
-  f = fopen(pathname, "w");
-  if (f == NULL)
-    {
-      perror(*argv);
-      eprintf("while opening the file: %s", pathname);
-      return 1;
-    }
+  if ((f = fopen(pathname, "w")) == NULL)
+    goto pfail;
   xsnprintf(piddata, "%u\n", getpid());
   if (fwrite(piddata, 1, strlen(piddata), f) < strlen(piddata))
     {
       fclose(f);
       if (unlink(pathname) < 0)
 	perror(*argv);
-      return -1;
+      return 1;
     }
   fflush(f);
   fclose(f);
   if (chmod(pathname, S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) < 0)
-    {
-      perror(*argv);
-      eprintf("while setting permissions for PID file: %s", pathname);
-    }
+    perror(*argv);
   
   /* Create data storage directory. */
   if (create_directory_root(MDS_STORAGE_ROOT_DIRECTORY))
@@ -228,32 +173,13 @@ int main(int argc_, char** argv_)
   strcpy(address.sun_path, pathname);
   unlink(pathname);
   fd = socket(AF_UNIX, SOCK_STREAM, 0);
-  if (fchmod(fd, S_IRWXU) < 0)
-    {
-      perror(*argv);
-      eprint("while making anonymous socket private to its owner.");
-      goto fail;
-    }
-  if (bind(fd, (struct sockaddr*)(&address), sizeof(address)) < 0)
-    {
-      perror(*argv);
-      eprintf("while binding socket to file: %s", pathname);
-      goto fail;
-    }
-  if (chown(pathname, getuid(), NOBODY_GROUP_GID) < 0)
-    {
-      perror(*argv);
-      eprint("while making socket private to the real user.");
-      goto fail;
-    }
+  if (fchmod(fd, S_IRWXU) < 0)                                      goto pfail;
+  if (bind(fd, (struct sockaddr*)(&address), sizeof(address)) < 0)  goto pfail;
+  if (chown(pathname, getuid(), NOBODY_GROUP_GID) < 0)              goto pfail;
   
   /* Start listening on socket. */
   if (listen(fd, SOMAXCONN) < 0)
-    {
-      perror(*argv);
-      eprintf("while setting up listening on socket: %s", pathname);
-      goto fail;
-    }
+    goto pfail;
   
   /* Start master server and respawn it if it crashes. */
   rc = spawn_and_respawn_server(fd);
@@ -279,6 +205,8 @@ int main(int argc_, char** argv_)
   
   return rc;
   
+ pfail:
+  perror(*argv);
  fail:
   rc = 1;
   goto done;
@@ -286,6 +214,64 @@ int main(int argc_, char** argv_)
 
 
 /**
+ * Read a PID-file and determine whether it refers to an non-existing process
+ * 
+ * @param   f  The PID-file
+ * @return     Whether the PID-file is not longer used
+ */
+int is_pid_file_reusable(FILE* f)
+{
+  char piddata[64];
+  size_t read_len;
+  
+  read_len = fread(piddata, 1, sizeof(piddata) / sizeof(char), f);
+  if (ferror(f)) /* Failed to read. */
+    perror(*argv);
+  else if (feof(f) == 0) /* Did not read everything. */
+    eprint("the content of a PID file is larger than expected.");
+  else
+    {
+      pid_t pid = parse_pid_t(piddata, read_len - 1);
+      if (pid == (pid_t)-1)
+	eprint("the content of a PID file is invalid.");
+      else
+	if (kill(pid, 0) < 0) /* Check if the PID is still allocated to any process. */
+	  return errno == ESRCH; /* PID is not used. */
+    }
+  
+  return 0;
+}
+
+
+/**
+ * Parse an LF-terminated string as a non-negative `pid_t`
+ * 
+ * @param   str  The string
+ * @param   n    The length of the string, excluding LF-termination
+ * @return       The pid, `(pid_t)-1` if malformated
+ */
+pid_t parse_pid_t(const char* str, size_t n)
+{
+  pid_t pid = 0;
+  size_t i;
+  
+  for (i = 0; i < n; i++)
+    {
+      char c = str[i];
+      if (('0' <= c) && (c <= '9'))
+	pid = pid * 10 + (c & 15);
+      else
+	return (pid_t)-1;
+    }
+  
+  if (str[n] != '\n')
+    return (pid_t)-1;
+  
+  return pid;
+}
+
+
+/**
  * Start master server and respawn it if it crashes
  * 
  * @param   fd  The file descriptor of the socket
@@ -322,7 +308,6 @@ int spawn_and_respawn_server(int fd)
       if (pid == (pid_t)-1)
 	{
 	  perror(*argv);
-	  eprint("while forking.");
 	  goto fail;
 	}
       
@@ -331,16 +316,12 @@ int spawn_and_respawn_server(int fd)
 	  /* Get the current time. (Start of child process.) */
 	  time_error = (monotone(&time_start) < 0);
 	  if (time_error)
-	    {
-	      perror(*argv);
-	      eprint("while reading a monotonic clock.");
-	    }
+	    perror(*argv);
 	  
 	  /* Wait for master server to die. */
 	  if (waitpid(pid, &status, 0) == (pid_t)-1)
 	    {
 	      perror(*argv);
-	      eprint("while waiting for child process to exit.");
 	      goto fail;
 	    }
 	  
@@ -376,7 +357,6 @@ int spawn_and_respawn_server(int fd)
 	      if (child_args[argc + 0] == NULL)
 		{
 		  perror(*argv);
-		  eprint("while duplicating string.");
 		  goto fail;
 		}
 	    }
@@ -389,14 +369,12 @@ int spawn_and_respawn_server(int fd)
 	  if (drop_privileges())
 	    {
 	      perror(*argv);
-	      eprint("while dropping privileges.");
 	      goto fail;
 	    }
 	  
 	  /* Start master server. */
 	  execv(master_server, child_args);
 	  perror(*argv);
-	  eprint("while changing execution image.");
 	  goto fail;
 	}
     }
@@ -440,7 +418,6 @@ int create_directory_root(const char* pathname)
 	  if (errno != EEXIST) /* Unlikely race condition. */
 	    {
 	      perror(*argv);
-	      eprintf("while creating directory: %s", pathname);
 	      return 1;
 	    }
 	}
@@ -449,7 +426,6 @@ int create_directory_root(const char* pathname)
 	if (chown(pathname, ROOT_USER_UID, ROOT_GROUP_GID) < 0)
 	  {
 	    perror(*argv);
-	    eprintf("while changing owner of directory: %s", pathname);
 	    return 1;
 	  }
     }
@@ -486,7 +462,6 @@ int create_directory_user(const char* pathname)
 	  if (errno != EEXIST) /* Unlikely race condition. */
 	    {
 	      perror(*argv);
-	      eprintf("while creating directory: %s", pathname);
 	      return 1;
 	    }
 	}
@@ -495,7 +470,6 @@ int create_directory_user(const char* pathname)
 	if (chown(pathname, getuid(), NOBODY_GROUP_GID) < 0)
 	  {
 	    perror(*argv);
-	    eprintf("while changing owner of directory: %s", pathname);
 	    return 1;
 	  }
     }
@@ -516,6 +490,7 @@ int unlink_recursive(const char* pathname)
   int rc = 0;
   struct dirent* file;
   
+  /* Check that we could examine the directory. */
   if (dir == NULL)
     {
       int errno_ = errno;
@@ -524,10 +499,10 @@ int unlink_recursive(const char* pathname)
 	return 0;
       errno = errno_;
       perror(*argv);
-      eprintf("while examining the content of directory: %s", pathname);
       return 1;
     }
   
+  /* Remove the content of the directory. */
   while ((file = readdir(dir)) != NULL)
     if (strcmp(file->d_name, ".") && strcmp(file->d_name, ".."))
       if (unlink(file->d_name) < 0)
@@ -537,17 +512,16 @@ int unlink_recursive(const char* pathname)
 	  else
 	    {
 	      perror(*argv);
-	      eprintf("while unlinking file: %s", file->d_name);
 	      rc = 1;
 	      goto done;
 	    }
 	  eprint("pop");
 	}
   
+  /* Remvoe the drectory. */
   if (rmdir(pathname) < 0)
     {
       perror(*argv);
-      eprintf("while removing directory: %s", pathname);
       rc = 1;
     }
   
diff --git a/src/mds.h b/src/mds.h
index 20b5f66..b998f35 100644
--- a/src/mds.h
+++ b/src/mds.h
@@ -19,6 +19,27 @@
 #define MDS_MDS_H
 
 
+#include <sys/types.h>
+#include <stdio.h>
+
+
+/**
+ * Read a PID-file and determine whether it refers to an non-existing process
+ * 
+ * @param   f  The PID-file
+ * @return     Whether the PID-file is not longer used
+ */
+int is_pid_file_reusable(FILE* f);
+
+/**
+ * Parse an LF-terminated string as a non-negative `pid_t`
+ * 
+ * @param   str  The string
+ * @param   n    The length of the string, excluding LF-termination
+ * @return       The pid, `(pid_t)-1` if malformated
+ */
+pid_t parse_pid_t(const char* str, size_t n) __attribute__((pure));
+
 /**
  * Start master server and respawn it if it crashes
  *