uffd.c: move the code out of the 'main' function

Most of the UFFD logic was in the function uffd_listen() which was
directly called from crtools.c. In preparation for the remote lazy
restore most of the code has been moved to separate function for better
integration of the network functionality.
Signed-off-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/uffd.c

@@ -486,38 +486,20 @@ out:
 	return ret;
 }
 
-int uffd_listen()
+static int handle_requests(int fd)
 {
-	__u64 address;
-	void *dest;
-	__u64 flags;
+	fd_set set;
+	int ret = -1;
 	struct uffd_msg msg;
+	__u64 flags;
+	__u64 address;
 	unsigned long ps;
-	int rc;
-	fd_set set;
 	struct timeval timeout;
-	int uffd;
-	int uffd_flags;
 	struct uffd_pages_struct *uffd_pages;
+	void *dest;
 
 	LIST_HEAD(uffd_list);
 
-	if (!opts.addr) {
-		pr_info("Please specify a file name for the unix domain socket\n");
-		pr_info("used to communicate between the lazy-pages server\n");
-		pr_info("and the restore process. Use the --address option like\n");
-		pr_info("criu --lazy-pages --address /tmp/userfault.socket\n");
-		return -1;
-	}
-
-	pr_debug("Waiting for incoming connections on %s\n", opts.addr);
-	if ((uffd = ud_open()) < 0)
-		exit(0);
-
-	pr_debug("uffd is 0x%d\n", uffd);
-	uffd_flags = fcntl(uffd, F_GETFD, NULL);
-	pr_debug("uffd_flags are 0x%x\n", uffd_flags);
-
 	/*
 	 * Find the memory pages belonging to the restored process
 	 * so that it is trackable when all pages have been transferred.
@@ -527,13 +509,13 @@ int uffd_listen()
 
 	/* Initialize FD sets for read() with timeouts (using select()) */
 	FD_ZERO(&set);
-	FD_SET(uffd, &set);
+	FD_SET(fd, &set);
 
 	/* All operations will be done on page size */
 	ps = page_size();
 	dest = xmalloc(ps);
 	if (!dest)
-		goto out;
+		return ret;
 
 	while (1) {
 		bool page_sent = false;
@@ -548,24 +530,25 @@ int uffd_listen()
 		 */
 		timeout.tv_sec = 5;
 		timeout.tv_usec = 0;
-		rc = select(uffd + 1, &set, NULL, NULL, &timeout);
-		pr_debug("select() rc: 0x%x\n", rc);
-		if (rc == 0) {
+		ret = select(fd + 1, &set, NULL, NULL, &timeout);
+		pr_debug("select() rc: 0x%x\n", ret);
+		if (ret == 0) {
 			pr_debug("read timeout\n");
 			pr_debug("switching from request to copy mode\n");
 			break;
 		}
-		rc = read(uffd, &msg, sizeof(msg));
-		pr_debug("read() rc: 0x%x\n", rc);
-
-		if (rc != sizeof(msg)) {
-			if (rc < 0)
-				pr_perror("read error");
-			else
-				pr_debug("short read\n");
-			continue;
+		ret = read(fd, &msg, sizeof(msg));
+		pr_debug("read() ret: 0x%x\n", ret);
+		if (!ret)
+			break;
+
+		if (ret != sizeof(msg)) {
+			pr_perror("Can't read userfaultfd message from socket");
+			ret = -1;
+			break;
 		}
 
+		ret = 0;
 		/* Align requested address to the next page boundary */
 		address = msg.arg.pagefault.address & ~(ps - 1);
 		pr_debug("msg.arg.pagefault.address 0x%llx\n", address);
@@ -588,37 +571,63 @@ int uffd_listen()
 
 		if (msg.event != UFFD_EVENT_PAGEFAULT) {
 			pr_err("unexpected msg event %u\n", msg.event);
-			rc = 1;
+			ret = -1;
 			goto out;
 		}
 
-		rc = handle_regular_pages(uffd, &uffd_list, dest, address);
-		if (rc < 0) {
+		ret = handle_regular_pages(fd, &uffd_list, dest, address);
+		if (ret < 0) {
 			pr_err("Error during regular page copy\n");
-			rc = 1;
+			ret = -1;
 			goto out;
 		}
 	}
 	pr_debug("Handle remaining pages\n");
-	rc = handle_remaining_pages(uffd, &uffd_list, dest);
-	if (rc < 0) {
+	ret = handle_remaining_pages(fd, &uffd_list, dest);
+	if (ret < 0) {
 		pr_err("Error during remaining page copy\n");
-		rc = 1;
+		ret = 1;
 		goto out;
 	}
 
 	pr_debug("With UFFD transferred pages: (%ld/%ld)\n", uffd_copied_pages, total_pages);
-	if (uffd_copied_pages != total_pages) {
+	if ((uffd_copied_pages != total_pages) && (total_pages > 0)) {
 		pr_warn("Only %ld of %ld pages transferred via UFFD\n", uffd_copied_pages,
 			total_pages);
 		pr_warn("Something probably went wrong.\n");
-		rc = 1;
+		ret = 1;
 		goto out;
 	}
-	rc = 0;
+	ret = 0;
 
 out:
 	free(dest);
-	close(uffd);
-	return rc;
+	close(fd);
+	return ret;
+
+}
+int uffd_listen()
+{
+	int uffd;
+	int uffd_flags;
+
+	LIST_HEAD(uffd_list);
+
+	if (!opts.addr) {
+		pr_info("Please specify a file name for the unix domain socket\n");
+		pr_info("used to communicate between the lazy-pages server\n");
+		pr_info("and the restore process. Use the --address option like\n");
+		pr_info("criu --lazy-pages --address /tmp/userfault.socket\n");
+		return -1;
+	}
+
+	pr_debug("Waiting for incoming connections on %s\n", opts.addr);
+	if ((uffd = ud_open()) < 0)
+		exit(0);
+
+	pr_debug("uffd is 0x%d\n", uffd);
+	uffd_flags = fcntl(uffd, F_GETFD, NULL);
+	pr_debug("uffd_flags are 0x%x\n", uffd_flags);
+
+	return handle_requests(uffd);
 }