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>

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));
 }
 
 /**