diff --git a/Rakefile b/Rakefile
index 59bbcc4..8e5cb5a 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1,6 +1,6 @@
 DEBUG  = true
 
-SOURCES = %w( flexnbd ioutil readwrite serve util parse )
+SOURCES = %w( flexnbd ioutil readwrite serve util parse control )
 OBJECTS = SOURCES.map { |s| "#{s}.o" }
 LIBS    = %w( pthread )
 CCFLAGS = %w( -Wall )
diff --git a/control.c b/control.c
new file mode 100644
index 0000000..bc0de7c
--- /dev/null
+++ b/control.c
@@ -0,0 +1,241 @@
+#include "params.h"
+#include "util.h"
+#include "ioutil.h"
+#include "parse.h"
+#include "readwrite.h"
+#include "bitset.h"
+
+#include <stdlib.h>
+#include <string.h>
+#include <sys/un.h>
+
+static const int longest_run = 8<<20;
+
+void* mirror_runner(void* serve_params_uncast)
+{
+	struct mode_serve_params *serve = (struct mode_serve_params*) serve_params_uncast;
+	
+	int pass;
+	struct bitset_mapping *map = serve->mirror->dirty_map;
+	
+	for (pass=0; pass < 7 /* biblical */; pass++) {
+		uint64_t current = 0;
+		
+		debug("mirror start pass=%d", pass);
+		
+		while (current < serve->size) {
+			int run = bitset_run_count(map, current, longest_run);
+			
+			debug("mirror current=%ld, run=%d", current, run);
+			
+			if (bitset_is_set_at(map, current)) {
+				debug("^^^ writing");
+				
+				/* dirty area */
+				socket_nbd_write(
+					serve->mirror->client, 
+					current,
+					run,
+					0,
+					serve->mirror->mapped + current
+				);
+				
+				bitset_clear_range(map, current, run);
+			}
+			current += run;
+		}
+	}
+	
+	return NULL;
+}
+
+
+void control_mirror(struct control_params* client)
+{
+	off64_t size, remote_size;
+	int fd, map_fd;
+	struct mirror_status *mirror;
+	union mysockaddr connect_to;
+	char s_ip_address[64], s_port[8];
+	
+	CLIENT_ERROR_ON_FAILURE(
+		read_until_newline(client->socket, s_ip_address, 64),
+		"Failed to read destination IP"
+	);
+	CLIENT_ERROR_ON_FAILURE(
+		read_until_newline(client->socket, s_port, 8),
+		"Failed to read destination port"
+	);
+		
+	if (parse_ip_to_sockaddr(&connect_to.generic, s_ip_address) == 0)
+		CLIENT_ERROR("Couldn't parse connection address '%s'", 
+		s_ip_address);
+	
+	connect_to.v4.sin_port = atoi(s_port);
+	if (connect_to.v4.sin_port < 0 || connect_to.v4.sin_port > 65535)
+		CLIENT_ERROR("Port number must be >= 0 and <= 65535");
+	connect_to.v4.sin_port = htobe16(connect_to.v4.sin_port);
+	
+	fd = socket_connect(&connect_to.generic); /* FIXME uses wrong error handler */
+	
+	remote_size = socket_nbd_read_hello(fd);
+	remote_size = remote_size; // shush compiler
+	
+	mirror = xmalloc(sizeof(struct mirror_status));
+	mirror->client = fd;
+	mirror->max_bytes_per_second = 0;
+	
+	CLIENT_ERROR_ON_FAILURE(
+		open_and_mmap(
+			client->serve->filename, 
+			&map_fd,
+			&size, 
+			(void**) &mirror->mapped
+		),
+		"Failed to open and mmap %s",
+		client->serve->filename
+	);
+	
+	mirror->dirty_map = bitset_alloc(size, 4096);
+	bitset_set_range(mirror->dirty_map, 0, size);
+	
+	client->serve->mirror = mirror;
+	
+	CLIENT_ERROR_ON_FAILURE( /* FIXME should free mirror on error */
+		pthread_create(
+			&mirror->thread, 
+			NULL, 
+			mirror_runner, 
+			client->serve
+		),
+		"Failed to create mirror thread"
+	);
+}
+
+void control_acl(struct control_params* client)
+{
+	int acl_entries = 0, parsed;
+	char** s_acl_entry = NULL;
+	struct ip_and_mask (*acl)[], (*old_acl)[];
+	
+	while (1) {
+		char entry[64];
+		int result = read_until_newline(client->socket, entry, 64);
+		if (result == -1)
+			goto done;
+		if (result == 1) /* blank line terminates */
+			break;
+		s_acl_entry = xrealloc(
+			s_acl_entry, 
+			++acl_entries * sizeof(struct s_acl_entry*)
+		);
+		s_acl_entry[acl_entries-1] = strdup(entry);
+		debug("acl_entry = '%s'", s_acl_entry[acl_entries-1]);
+	}
+	
+	parsed = parse_acl(&acl, acl_entries, s_acl_entry);
+	if (parsed != acl_entries) {
+		write(client->socket, "error: ", 7);
+		write(client->socket, s_acl_entry[parsed], 
+		  strlen(s_acl_entry[parsed]));
+		write(client->socket, "\n", 1);
+		free(acl);
+	}
+	else {
+		old_acl = client->serve->acl;
+		client->serve->acl = acl;
+		client->serve->acl_entries = acl_entries;
+		free(old_acl);
+		write(client->socket, "ok\n", 3);
+	}
+	
+done:	if (acl_entries > 0) {
+		int i;
+		for (i=0; i<acl_entries; i++)
+			free(s_acl_entry[i]);
+		free(s_acl_entry);
+	}
+	return;
+}
+
+void control_status(struct control_params* client)
+{
+}
+void* control_serve(void* client_uncast)
+{
+	const int max = 256;
+	char command[max];
+	struct control_params* client = (struct control_params*) client_uncast;
+	
+	while (1) {
+		CLIENT_ERROR_ON_FAILURE(
+			read_until_newline(client->socket, command, max),
+			"Error reading command"
+		);
+		
+		if (strcmp(command, "acl") == 0)
+			control_acl(client);
+		else if (strcmp(command, "mirror") == 0)
+			control_mirror(client);
+		else if (strcmp(command, "status") == 0)
+			control_status(client);
+		else {
+			write(client->socket, "error: unknown command\n", 23);
+			break;
+		}
+	}
+	
+	close(client->socket);
+	free(client);
+	return NULL;
+}
+
+void accept_control_connection(struct mode_serve_params* params, int client_fd, struct sockaddr* client_address)
+{
+	pthread_t control_thread;
+	struct control_params* control_params;
+	
+	control_params = xmalloc(sizeof(struct control_params));
+	control_params->socket = client_fd;
+	control_params->serve = params;
+
+	SERVER_ERROR_ON_FAILURE(
+		pthread_create(
+			&control_thread, 
+			NULL, 
+			control_serve, 
+			control_params
+		),
+		"Failed to create client thread"
+	);
+}
+
+void serve_open_control_socket(struct mode_serve_params* params)
+{
+	struct sockaddr_un bind_address;
+	
+	if (!params->control_socket_name)
+		return;
+
+	params->control = socket(AF_UNIX, SOCK_STREAM, 0);
+	SERVER_ERROR_ON_FAILURE(params->control,
+	  "Couldn't create control socket");
+	
+	memset(&bind_address, 0, sizeof(bind_address));
+	bind_address.sun_family = AF_UNIX;
+	strcpy(bind_address.sun_path, params->control_socket_name);
+	
+	unlink(params->control_socket_name); /* ignore failure */
+	
+	SERVER_ERROR_ON_FAILURE(
+		bind(params->control, &bind_address, sizeof(bind_address)),
+		"Couldn't bind control socket to %s",
+		params->control_socket_name
+	);
+	
+	SERVER_ERROR_ON_FAILURE(
+		listen(params->control, 5),
+		"Couldn't listen on control socket"
+	);
+}
+
diff --git a/control.h b/control.h
new file mode 100644
index 0000000..ab03fab
--- /dev/null
+++ b/control.h
@@ -0,0 +1,8 @@
+#ifndef __CONTROL_H
+#define __CONTROL_H
+
+void accept_control_connection(struct mode_serve_params* params, int client_fd, struct sockaddr* client_address);
+void serve_open_control_socket(struct mode_serve_params* params);
+
+#endif
+
diff --git a/flexnbd.c b/flexnbd.c
index 71047ff..2548340 100644
--- a/flexnbd.c
+++ b/flexnbd.c
@@ -130,6 +130,11 @@ void do_serve(struct mode_serve_params* params);
 void do_read(struct mode_readwrite_params* params);
 void do_write(struct mode_readwrite_params* params);
 
+union mode_params {
+	struct mode_serve_params serve;
+	struct mode_readwrite_params readwrite;
+};
+
 void mode(char* mode, int argc, char **argv)
 {
 	union mode_params params;
diff --git a/ioutil.c b/ioutil.c
index d61fcce..ef5d5a3 100644
--- a/ioutil.c
+++ b/ioutil.c
@@ -154,7 +154,7 @@ int splice_via_pipe_loop(int fd_in, int fd_out, size_t len)
 		/*if (run > 65535)
 			run = 65535;*/
 		r1 = splice(fd_in, NULL, pipefd[1], NULL, run, SPLICE_F_MORE|SPLICE_F_MOVE|SPLICE_F_NONBLOCK);
-		debug("%d", r1);
+		debug("%ld", r1);
 		if (r1 <= 0)
 			break;
 		r2 = splice(pipefd[0], NULL, fd_out, NULL, r1, SPLICE_F_MORE|SPLICE_F_MOVE);
diff --git a/params.h b/params.h
index 6c50b7f..5c1583b 100644
--- a/params.h
+++ b/params.h
@@ -59,10 +59,5 @@ struct client_params {
 	struct mode_serve_params* serve; /* FIXME: remove above duplication */
 };
 
-union mode_params {
-	struct mode_serve_params serve;
-	struct mode_readwrite_params readwrite;
-};
-
 #endif
 
diff --git a/serve.c b/serve.c
index fb77abe..df4c879 100644
--- a/serve.c
+++ b/serve.c
@@ -3,8 +3,7 @@
 #include "ioutil.h"
 #include "util.h"
 #include "bitset.h"
-#include "parse.h"
-#include "readwrite.h"
+#include "control.h"
 
 #include <sys/types.h>
 #include <sys/stat.h>
@@ -269,186 +268,6 @@ void* client_serve(void* client_uncast)
 	return NULL;
 }
 
-void control_acl(struct control_params* client)
-{
-	int acl_entries = 0, parsed;
-	char** s_acl_entry = NULL;
-	struct ip_and_mask (*acl)[], (*old_acl)[];
-	
-	while (1) {
-		char entry[64];
-		int result = read_until_newline(client->socket, entry, 64);
-		if (result == -1)
-			goto done;
-		if (result == 1) /* blank line terminates */
-			break;
-		s_acl_entry = xrealloc(
-			s_acl_entry, 
-			++acl_entries * sizeof(struct s_acl_entry*)
-		);
-		s_acl_entry[acl_entries-1] = strdup(entry);
-		debug("acl_entry = '%s'", s_acl_entry[acl_entries-1]);
-	}
-	
-	parsed = parse_acl(&acl, acl_entries, s_acl_entry);
-	if (parsed != acl_entries) {
-		write(client->socket, "error: ", 7);
-		write(client->socket, s_acl_entry[parsed], 
-		  strlen(s_acl_entry[parsed]));
-		write(client->socket, "\n", 1);
-		free(acl);
-	}
-	else {
-		old_acl = client->serve->acl;
-		client->serve->acl = acl;
-		client->serve->acl_entries = acl_entries;
-		free(old_acl);
-		write(client->socket, "ok\n", 3);
-	}
-	
-done:	if (acl_entries > 0) {
-		int i;
-		for (i=0; i<acl_entries; i++)
-			free(s_acl_entry[i]);
-		free(s_acl_entry);
-	}
-	return;
-}
-
-static const int longest_run = 8<<20;
-
-void* mirror_runner(void* serve_params_uncast)
-{
-	struct mode_serve_params *serve = (struct mode_serve_params*) serve_params_uncast;
-	
-	int pass;
-	struct bitset_mapping *map = serve->mirror->dirty_map;
-	
-	for (pass=0; pass < 7 /* biblical */; pass++) {
-		uint64_t current = 0;
-		
-		debug("mirror start pass=%d", pass);
-		
-		while (current < serve->size) {
-			int run = bitset_run_count(map, current, longest_run);
-			
-			debug("mirror current=%d, run=%d", current, run);
-			
-			if (bitset_is_set_at(map, current)) {
-				debug("^^^ writing", current, run);
-				
-				/* dirty area */
-				socket_nbd_write(
-					serve->mirror->client, 
-					current,
-					run,
-					0,
-					serve->mirror->mapped + current
-				);
-				
-				bitset_clear_range(map, current, run);
-			}
-			current += run;
-		}
-	}
-	
-	return NULL;
-}
-
-void control_mirror(struct control_params* client)
-{
-	off64_t size, remote_size;
-	int fd, map_fd;
-	struct mirror_status *mirror;
-	union mysockaddr connect_to;
-	char s_ip_address[64], s_port[8];
-	
-	CLIENT_ERROR_ON_FAILURE(
-		read_until_newline(client->socket, s_ip_address, 64),
-		"Failed to read destination IP"
-	);
-	CLIENT_ERROR_ON_FAILURE(
-		read_until_newline(client->socket, s_port, 8),
-		"Failed to read destination port"
-	);
-		
-	if (parse_ip_to_sockaddr(&connect_to.generic, s_ip_address) == 0)
-		CLIENT_ERROR("Couldn't parse connection address '%s'", 
-		s_ip_address);
-	
-	connect_to.v4.sin_port = atoi(s_port);
-	if (connect_to.v4.sin_port < 0 || connect_to.v4.sin_port > 65535)
-		CLIENT_ERROR("Port number must be >= 0 and <= 65535");
-	connect_to.v4.sin_port = htobe16(connect_to.v4.sin_port);
-	
-	fd = socket_connect(&connect_to.generic); /* FIXME uses wrong error handler */
-	
-	remote_size = socket_nbd_read_hello(fd);
-	
-	mirror = xmalloc(sizeof(struct mirror_status));
-	mirror->client = fd;
-	mirror->max_bytes_per_second = 0;
-	
-	CLIENT_ERROR_ON_FAILURE(
-		open_and_mmap(
-			client->serve->filename, 
-			&map_fd,
-			&size, 
-			(void**) &mirror->mapped
-		),
-		"Failed to open and mmap %s",
-		client->serve->filename
-	);
-	
-	mirror->dirty_map = bitset_alloc(size, block_allocation_resolution);
-	bitset_set_range(mirror->dirty_map, 0, size);
-	
-	client->serve->mirror = mirror;
-	
-	CLIENT_ERROR_ON_FAILURE( /* FIXME should free mirror on error */
-		pthread_create(
-			&mirror->thread, 
-			NULL, 
-			mirror_runner, 
-			client->serve
-		),
-		"Failed to create mirror thread"
-	);
-}
-
-void control_status(struct control_params* client)
-{
-}
-
-void* control_serve(void* client_uncast)
-{
-	const int max = 256;
-	char command[max];
-	struct control_params* client = (struct control_params*) client_uncast;
-	
-	while (1) {
-		CLIENT_ERROR_ON_FAILURE(
-			read_until_newline(client->socket, command, max),
-			"Error reading command"
-		);
-		
-		if (strcmp(command, "acl") == 0)
-			control_acl(client);
-		else if (strcmp(command, "mirror") == 0)
-			control_mirror(client);
-		else if (strcmp(command, "status") == 0)
-			control_status(client);
-		else {
-			write(client->socket, "error: unknown command\n", 23);
-			break;
-		}
-	}
-	
-	close(client->socket);
-	free(client);
-	return NULL;
-}
-
 static int testmasks[9] = { 0,128,192,224,240,248,252,254,255 };
 
 int is_included_in_acl(int list_length, struct ip_and_mask (*list)[], struct sockaddr* test)
@@ -524,35 +343,6 @@ void serve_open_server_socket(struct mode_serve_params* params)
 	);
 }
 
-void serve_open_control_socket(struct mode_serve_params* params)
-{
-	struct sockaddr_un bind_address;
-	
-	if (!params->control_socket_name)
-		return;
-
-	params->control = socket(AF_UNIX, SOCK_STREAM, 0);
-	SERVER_ERROR_ON_FAILURE(params->control,
-	  "Couldn't create control socket");
-	
-	memset(&bind_address, 0, sizeof(bind_address));
-	bind_address.sun_family = AF_UNIX;
-	strcpy(bind_address.sun_path, params->control_socket_name);
-	
-	unlink(params->control_socket_name); /* ignore failure */
-	
-	SERVER_ERROR_ON_FAILURE(
-		bind(params->control, &bind_address, sizeof(bind_address)),
-		"Couldn't bind control socket to %s",
-		params->control_socket_name
-	);
-	
-	SERVER_ERROR_ON_FAILURE(
-		listen(params->control, 5),
-		"Couldn't listen on control socket"
-	);
-}
-
 void accept_nbd_client(struct mode_serve_params* params, int client_fd, struct sockaddr* client_address)
 {
 	pthread_t client_thread;
@@ -585,26 +375,6 @@ void accept_nbd_client(struct mode_serve_params* params, int client_fd, struct s
 	/* FIXME: maybe shouldn't be fatal? */
 }
 
-void accept_control_connection(struct mode_serve_params* params, int client_fd, struct sockaddr* client_address)
-{
-	pthread_t control_thread;
-	struct control_params* control_params;
-	
-	control_params = xmalloc(sizeof(struct control_params));
-	control_params->socket = client_fd;
-	control_params->serve = params;
-
-	SERVER_ERROR_ON_FAILURE(
-		pthread_create(
-			&control_thread, 
-			NULL, 
-			control_serve, 
-			control_params
-		),
-		"Failed to create client thread"
-	);
-}
-
 void serve_accept_loop(struct mode_serve_params* params) 
 {
 	while (1) {