zdtm: check c/r of fds on unmounted mounts

We check that fds to files and directories opened on unmounted
mounts (unmount2(MNT_DETACH)) are restored correctly.

Signed-off-by: Bhavik Sachdev <b.sachdev1904@gmail.com>

test/zdtm/static/Makefile

@@ -398,6 +398,7 @@ TST_DIR		=				\
 		cwd00				\
 		cwd01				\
 		cwd02				\
+		unmounted_mount			\
 		unmounted_bind_mount		\
 		overmount_dev			\
 		overmount_file			\

test/zdtm/static/unmounted_mount.c

@@ -0,0 +1,140 @@
+#include <fcntl.h>
+#include <linux/limits.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#include "zdtmtst.h"
+
+const char *test_doc = "Check C/R of fds to files, directories on unmounted mounts";
+const char *test_author = "Bhavik Sachdev <b.sachdev1904@gmail.com>";
+
+char *dirname;
+TEST_OPTION(dirname, string, "directory name", 1);
+
+#define MOUNT_POINT "mnt"
+#define SUBDIR	    "mnt/subdir"
+#define FILE	    "mnt/file"
+
+#define BUFLEN 1000
+
+static int get_subdir_fd(void)
+{
+	int fd = -1;
+	if (mkdir(SUBDIR, 0700)) {
+		pr_perror("mkdir %s", SUBDIR);
+		return -1;
+	}
+	fd = open(SUBDIR, O_DIRECTORY);
+	if (fd < 0) {
+		pr_perror("open %s", SUBDIR);
+		return -1;
+	}
+	return fd;
+}
+
+static int get_file_fd(uint32_t *crc)
+{
+	uint8_t buf[BUFLEN];
+	int fd = -1;
+
+	fd = open(FILE, O_CREAT | O_RDWR, 0644);
+	if (fd < 0) {
+		pr_perror("open %s", FILE);
+		return -1;
+	}
+	datagen(buf, BUFLEN, crc);
+	if (write(fd, buf, BUFLEN) != BUFLEN) {
+		pr_perror("write %s", FILE);
+		close(fd);
+		return -1;
+	}
+	return fd;
+}
+
+int main(int argc, char *argv[])
+{
+	int subdir_fd = -1, file_fd = -1, ret = 1;
+	uint32_t crc = ~0;
+	uint8_t buf[BUFLEN];
+	struct stat st;
+
+	test_init(argc, argv);
+
+	if (mkdir(dirname, 0700)) {
+		pr_perror("mkdir %s", dirname);
+		return 1;
+	}
+
+	if (chdir(dirname)) {
+		pr_perror("chdir %s", dirname);
+		return 1;
+	}
+
+	if (mkdir(MOUNT_POINT, 0700)) {
+		pr_perror("mkdir %s", MOUNT_POINT);
+		return 1;
+	}
+
+	if (mount("none", MOUNT_POINT, "tmpfs", 0, NULL)) {
+		pr_perror("mount %s", MOUNT_POINT);
+		return 1;
+	}
+
+	subdir_fd = get_subdir_fd();
+	if (subdir_fd < 0)
+		goto err;
+
+	file_fd = get_file_fd(&crc);
+	if (file_fd < 0)
+		goto err;
+
+	if (umount2(MOUNT_POINT, MNT_DETACH)) {
+		pr_perror("umount2 %s", MOUNT_POINT);
+		goto err;
+	}
+
+	test_daemon();
+	test_waitsig();
+
+	/* Should still be able to read from the fd */
+	if (lseek(file_fd, 0, SEEK_SET)) {
+		pr_perror("lseek %s", FILE);
+		goto out;
+	}
+
+	if (read(file_fd, buf, BUFLEN) != BUFLEN) {
+		pr_perror("read %s", FILE);
+		ret = 1;
+		goto out;
+	}
+
+	crc = ~0;
+	if (datachk(buf, BUFLEN, &crc)) {
+		fail("Data mismatch");
+		goto out;
+	}
+
+	if (fstat(subdir_fd, &st)) {
+		fail("could not stat dir fd");
+		goto out;
+	}
+
+	if (S_ISDIR(st.st_mode)) {
+		ret = 0;
+		pass();
+		goto out;
+	} else {
+		fail("dir fd does not point to a dir");
+		goto out;
+	}
+err:
+	umount(MOUNT_POINT);
+out:
+	chdir("..");
+	if (subdir_fd > 0)
+		close(subdir_fd);
+	if (file_fd > 0)
+		close(file_fd);
+	return ret;
+}

test/zdtm/static/unmounted_mount.desc

@@ -0,0 +1 @@
+{'flags': 'suid crfail', 'flavor': 'ns uns'}