mount: Fix trailing / when a file is bind-mounted

E.g. I have a /etc/hosts in workspace mounted from the host, and get the following message.

(00.141008)      1: mnt-v2: Create plain mountpoint /tmp/.criu.mntns.K1biY1/mnt-0000000938 for 938
(00.141546)      1: mnt-v2:     Mounting unsupported @938 (0)
(00.141887)      1: mnt-v2:     Bind /tmp/agent/1-d8c746c6fda3a8b2/workspace/etc/hosts/ to /tmp/.criu.mntns.K1biY1/mnt-0000000938
(00.142179)      1: Error (criu/mount-v2.c:319): mnt-v2: Failed to open_tree /tmp/agent/1-d8c746c6fda3a8b2/workspace/etc/hosts/: Not a directory
(00.143774) Error (criu/cr-restore.c:2320): Restoring FAILED.

Signed-off-by: Chuan Qiu <[email protected]>

Author: eagleonhill

criu/mount.c

@@ -888,7 +888,11 @@ static int resolve_external_mounts(struct mount_info *info)
 
 		cut_root = cut_root_for_bind(m->root, match->root);
 
-		p = xsprintf("%s/%s", match->ns_mountpoint + 1, cut_root);
+		if (cut_root[0] == '\0') {
+			p = xstrdup(match->ns_mountpoint + 1);
+		} else {
+			p = xsprintf("%s/%s", match->ns_mountpoint + 1, cut_root);
+		}
 		if (!p)
 			return -1;
 

test/zdtm/static/Makefile

@@ -442,6 +442,7 @@ TST_DIR		=				\
 		mnt_ext_root			\
 		mnt_root_ext			\
 		mnt_ext_collision		\
+		mntns_file_bind_same_root \
 		mntns_pivot_root		\
 		mntns_pivot_root_ro		\
 		mnt_ext_sharing			\

test/zdtm/static/mntns_file_bind_same_root.c

@@ -0,0 +1,92 @@
+#include <sched.h>
+#include <signal.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <linux/limits.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include "zdtmtst.h"
+#include "lock.h"
+
+const char *test_doc = "Check bind mount for file with multiple mount-points can be restored.";
+const char *test_author = "Chuan Qiu <[email protected]>";
+
+char *dirname = "mntns_file_bind_same_root.test";
+TEST_OPTION(dirname, string, "directory name", 1);
+
+char *source = "mntns_file_bind_same_root";
+
+int main(int argc, char **argv)
+{
+	char *testfile = "testfile_mnt";
+	char testfile_mounted[PATH_MAX];
+
+	int fd;
+	char *zdtm_newns = getenv("ZDTM_NEWNS");
+
+	snprintf(testfile_mounted, sizeof(testfile_mounted), "%s/%s", dirname, testfile);
+
+	if (!zdtm_newns) {
+		pr_perror("ZDTM_NEWNS is not set");
+		return 1;
+	} else if (strcmp(zdtm_newns, "1")) {
+		goto test;
+	}
+
+	fd = open(testfile, O_RDWR | O_CREAT, 0666);
+	if (fd < 0) {
+		pr_perror("open");
+		goto err;
+	}
+	write(fd, "test data", 9);
+	close(fd);
+
+	// Mount a file bind mount in a shared mountpoint.
+	mkdir(dirname, 0755);
+
+	if (mount(source, dirname, "tmpfs", 0, NULL)) {
+		pr_perror("mount tmpfs");
+		goto err;
+	}
+
+	if (mount(NULL, dirname, NULL, MS_SHARED, NULL)) {
+		pr_perror("make shared");
+		goto err;
+	}
+
+	fd = open(testfile_mounted, O_RDWR | O_CREAT, 0666);
+	if (fd < 0) {
+		pr_perror("open");
+		goto err;
+	}
+	close(fd);
+
+test:
+	test_init(argc, argv);
+
+	if (mount(testfile, testfile_mounted, NULL, MS_BIND, NULL)) {
+		pr_perror("mount bind file %s to %s",
+			  testfile, testfile_mounted);
+		goto err;
+	}
+	if (unshare(CLONE_NEWNS)) {
+		pr_perror("unshare");
+		goto err;
+	}
+	// This will create a file mount with same root path.
+	if (mount(NULL, "/", NULL, MS_REC | MS_SLAVE, NULL)) {
+		pr_perror("make private");
+		goto err;
+	}
+	test_daemon();
+	test_waitsig();
+	pass();
+	return 0;
+err:
+	return 1;
+}

test/zdtm/static/mntns_file_bind_same_root.desc

@@ -0,0 +1 @@
+{'feature': 'mnt_id', 'flavor': 'ns', 'flags': 'suid', 'opts': '--external mnt[]:m --enable-external-masters'}