remote: Refactor TCP server setup

The function `setup_TCP_server_socket` (defined in img-remote.c) and
`setup_tcp_server` (defined in util.c) have very similar functionality.

Replace setup_TCP_server_socket() with setup_tcp_server() to reduce
code duplication and to enable IPv6 support for the image-cache action
of CRIU.

We set SO_REUSEADDR flag to allow reuse of local addresses.
Signed-off-by: Radostin Stoyanov <rstoyanov1@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/include/util.h

@@ -289,7 +289,7 @@ char *xsprintf(const char *fmt, ...)
 
 void print_data(unsigned long addr, unsigned char *data, size_t size);
 
-int setup_tcp_server(char *type);
+int setup_tcp_server(char *type, char *addr, unsigned short *port);
 int run_tcp_server(bool daemon_mode, int *ask, int cfd, int sk);
 int setup_tcp_client(char *addr);
 

criu/page-xfer.c

@@ -991,7 +991,7 @@ int cr_page_server(bool daemon_mode, bool lazy_dump, int cfd)
 		goto no_server;
 	}
 
-	sk = setup_tcp_server("page");
+	sk = setup_tcp_server("page", opts.addr, &opts.port);
 	if (sk == -1)
 		return -1;
 no_server:

criu/util.c

@@ -1245,7 +1245,8 @@ void print_data(unsigned long addr, unsigned char *data, size_t size)
 	}
 }
 
-static int get_sockaddr_in(struct sockaddr_storage *addr, char *host)
+static int get_sockaddr_in(struct sockaddr_storage *addr, char *host,
+			unsigned short port)
 {
 	memset(addr, 0, sizeof(*addr));
 
@@ -1262,25 +1263,26 @@ static int get_sockaddr_in(struct sockaddr_storage *addr, char *host)
 	}
 
 	if (addr->ss_family == AF_INET6) {
-		((struct sockaddr_in6 *)addr)->sin6_port = htons(opts.port);
+		((struct sockaddr_in6 *)addr)->sin6_port = htons(port);
 	} else if (addr->ss_family == AF_INET) {
-		((struct sockaddr_in *)addr)->sin_port = htons(opts.port);
+		((struct sockaddr_in *)addr)->sin_port = htons(port);
 	}
 
 	return 0;
 }
 
-int setup_tcp_server(char *type)
+int setup_tcp_server(char *type, char *addr, unsigned short *port)
 {
 	int sk = -1;
+	int sockopt = 1;
 	struct sockaddr_storage saddr;
 	socklen_t slen = sizeof(saddr);
 
-	if (get_sockaddr_in(&saddr, opts.addr)) {
+	if (get_sockaddr_in(&saddr, addr, (*port))) {
 		return -1;
 	}
 
-	pr_info("Starting %s server on port %u\n", type, opts.port);
+	pr_info("Starting %s server on port %u\n", type, *port);
 
 	sk = socket(saddr.ss_family, SOCK_STREAM, IPPROTO_TCP);
 
@@ -1289,6 +1291,12 @@ int setup_tcp_server(char *type)
 		return -1;
 	}
 
+	if (setsockopt(
+		sk, SOL_SOCKET, SO_REUSEADDR, &sockopt, sizeof(sockopt)) == -1) {
+		pr_perror("Unable to set SO_REUSEADDR");
+		goto out;
+	}
+
 	if (bind(sk, (struct sockaddr *)&saddr, slen)) {
 		pr_perror("Can't bind %s server", type);
 		goto out;
@@ -1300,19 +1308,19 @@ int setup_tcp_server(char *type)
 	}
 
 	/* Get socket port in case of autobind */
-	if (opts.port == 0) {
+	if ((*port) == 0) {
 		if (getsockname(sk, (struct sockaddr *)&saddr, &slen)) {
 			pr_perror("Can't get %s server name", type);
 			goto out;
 		}
 
 		if (saddr.ss_family == AF_INET6) {
-			opts.port = ntohs(((struct sockaddr_in6 *)&saddr)->sin6_port);
+			(*port) = ntohs(((struct sockaddr_in *)&saddr)->sin_port);
 		} else if (saddr.ss_family == AF_INET) {
-			opts.port = ntohs(((struct sockaddr_in *)&saddr)->sin_port);
+			(*port) = ntohs(((struct sockaddr_in6 *)&saddr)->sin6_port);
 		}
 
-		pr_info("Using %u port\n", opts.port);
+		pr_info("Using %u port\n", (*port));
 	}
 
 	return sk;
@@ -1375,7 +1383,7 @@ int setup_tcp_client(char *addr)
 
 	pr_info("Connecting to server %s:%u\n", addr, opts.port);
 
-	if (get_sockaddr_in(&saddr, addr))
+	if (get_sockaddr_in(&saddr, addr, opts.port))
 		return -1;
 
 	sk = socket(saddr.ss_family, SOCK_STREAM, IPPROTO_TCP);