util: Make ns_enter() a void function and report setns() errors

ns_enter() returns an integer... but it's always zero.  If we actually fail
the function doesn't return.  Therefore it makes more sense for this to be
a function returning void, and we can remove the cases where we pointlessly
checked its return value.

In addition ns_enter() is usually called from an ephemeral thread created
by NS_CALL().  That means that the exit(EXIT_FAILURE) there usually won't
be reported (since NS_CALL() doesn't wait() for the thread).  So, use die()
instead to print out some information in the unlikely event that our
setns() here does fail.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

conf.c

@@ -101,9 +101,10 @@ static int get_bound_ports_ns(void *arg)
 	struct get_bound_ports_ns_arg *a = (struct get_bound_ports_ns_arg *)arg;
 	struct ctx *c = a->c;
 
-	if (!c->pasta_netns_fd || ns_enter(c))
+	if (!c->pasta_netns_fd)
 		return 0;
 
+	ns_enter(c);
 	get_bound_ports(c, 1, a->proto);
 
 	return 0;

tap.c

@@ -1182,9 +1182,9 @@ static int tap_ns_tun(void *arg)
 	struct ctx *c = (struct ctx *)arg;
 
 	memcpy(ifr.ifr_name, c->pasta_ifn, IFNAMSIZ);
+	ns_enter(c);
 
-	if (ns_enter(c) ||
-	    (tun_ns_fd = open("/dev/net/tun", flags)) < 0 ||
+	if ((tun_ns_fd = open("/dev/net/tun", flags)) < 0 ||
 	    ioctl(tun_ns_fd, TUNSETIFF, &ifr) ||
 	    !(c->pasta_ifi = if_nametoindex(c->pasta_ifn))) {
 		if (tun_ns_fd != -1)

udp.c

@@ -473,8 +473,7 @@ static int udp_splice_new_ns(void *arg)
 
 	a = (struct udp_splice_new_ns_arg *)arg;
 
-	if (ns_enter(a->c))
-		return 0;
+	ns_enter(a->c);
 
 	a->s = udp_splice_new(a->c, a->v6, a->src, true);
 
@@ -1064,8 +1063,7 @@ int udp_sock_init_ns(void *arg)
 	struct ctx *c = (struct ctx *)arg;
 	unsigned dst;
 
-	if (ns_enter(c))
-		return 0;
+	ns_enter(c);
 
 	for (dst = 0; dst < NUM_PORTS; dst++) {
 		if (!bitmap_isset(c->udp.fwd_out.f.map, dst))

util.c

@@ -378,16 +378,14 @@ void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version, int ns,
  * ns_enter() - Enter configured user (unless already joined) and network ns
  * @c:		Execution context
  *
- * Return: 0, won't return on failure
+ * Won't return on failure
  *
  * #syscalls:pasta setns
  */
-int ns_enter(const struct ctx *c)
+void ns_enter(const struct ctx *c)
 {
 	if (setns(c->pasta_netns_fd, CLONE_NEWNET))
-		exit(EXIT_FAILURE);
-
-	return 0;
+		die("setns() failed entering netns: %s", strerror(errno));
 }
 
 /**

util.h

@@ -216,7 +216,7 @@ int bitmap_isset(const uint8_t *map, int bit);
 char *line_read(char *buf, size_t len, int fd);
 void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version, int ns,
 			uint8_t *map, uint8_t *exclude);
-int ns_enter(const struct ctx *c);
+void ns_enter(const struct ctx *c);
 bool ns_is_init(void);
 void write_pidfile(int fd, pid_t pid);
 int __daemon(int pidfile_fd, int devnull_fd);