[LTP] [PATCH] syscalls/unshare: New test: CLONE_NEWNS unshares fs info

[lufei]

Add test case unshare04, to verify unshare(CLONE_NEWNS) also unshares
filesystem information.

Signed-off-by: lufei <lufei@uniontech.com>
---
 runtest/syscalls                              |  1 +
 testcases/kernel/syscalls/unshare/.gitignore  |  1 +
 testcases/kernel/syscalls/unshare/unshare04.c | 69 +++++++++++++++++++
 3 files changed, 71 insertions(+)
 create mode 100644 testcases/kernel/syscalls/unshare/unshare04.c

diff --git a/runtest/syscalls b/runtest/syscalls
index 844ae7a13..57338297a 100644
--- a/runtest/syscalls
+++ b/runtest/syscalls
@@ -1725,6 +1725,7 @@ unlinkat01 unlinkat01
 unshare01 unshare01
 unshare02 unshare02
 unshare03 unshare03
+unshare04 unshare04
 
 #
 # These tests require an unmounted block device
diff --git a/testcases/kernel/syscalls/unshare/.gitignore b/testcases/kernel/syscalls/unshare/.gitignore
index e5b5c261d..b1206e452 100644
--- a/testcases/kernel/syscalls/unshare/.gitignore
+++ b/testcases/kernel/syscalls/unshare/.gitignore
@@ -1,3 +1,4 @@
 /unshare01
 /unshare02
 /unshare03
+/unshare04
diff --git a/testcases/kernel/syscalls/unshare/unshare04.c b/testcases/kernel/syscalls/unshare/unshare04.c
new file mode 100644
index 000000000..0bbb9d19d
--- /dev/null
+++ b/testcases/kernel/syscalls/unshare/unshare04.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2025 lufei <lufei@uniontech.com>
+ */
+
+/*\
+ * This test case is to verify unshare(CLONE_NEWNS) also unshares filesystem
+ * information.
+ *
+ */
+
+#define _GNU_SOURCE
+
+#include "tst_test.h"
+#include "lapi/sched.h"
+
+#ifdef HAVE_UNSHARE
+
+#define TMP "/tmp"
+
+static void run(void)
+{
+	char *c_cwd;
+	char *p_cwd;
+	size_t size = 1024;
+
+	c_cwd = SAFE_MMAP(NULL, size, PROT_READ | PROT_WRITE,
+			MAP_SHARED | MAP_ANONYMOUS,
+			-1, 0);
+
+	p_cwd = SAFE_MALLOC(size);
+
+	struct tst_clone_args args = {
+		.flags = CLONE_FS,
+		.exit_signal = SIGCHLD,
+	};
+
+	if (!SAFE_CLONE(&args)) {
+
+		TST_EXP_PASS(unshare(CLONE_NEWNS));
+
+		SAFE_CHDIR(TMP);
+		SAFE_GETCWD(c_cwd, size);
+	} else {
+		SAFE_WAIT(NULL);
+
+		SAFE_GETCWD(p_cwd, size);
+
+		tst_res(TDEBUG, "parent cwd: %s", p_cwd);
+		tst_res(TDEBUG, "child cwd: %s", c_cwd);
+
+		//in parent, cwd stays in tst_tmpdir_path than TMP.
+		if (strcmp(p_cwd, c_cwd) == 0)
+			tst_res(TFAIL, "cwd not unshared as expected");
+		else
+			tst_res(TPASS, "cwd unshared");
+	}
+}
+
+static struct tst_test test = {
+	.forks_child = 1,
+	.needs_root = 1,
+	.needs_tmpdir = 1,
+	.test_all = run,
+};
+
+#else
+TST_TEST_TCONF("unshare syscall is undefined.");
+#endif
-- 
2.39.3