selftests: tty: add selftest for tty timestamp updates

Add new test case which checks that timestamp updates on actual terminal
character device (e.g. /dev/pts/0) happen even if the terminal is
accessed via magic /dev/tty file.

Signed-off-by: Michal Sekletar <[e-mail]>
Message-ID: <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

tools/testing/selftests/Makefile

···
 endif
 TARGETS += tmpfs
 TARGETS += tpm2
+TARGETS += tty
 TARGETS += user
 TARGETS += vDSO
 TARGETS += mm

tools/testing/selftests/tty/.gitignore

···
+# SPDX-License-Identifier: GPL-2.0-only
+tty_tstamp_update

tools/testing/selftests/tty/Makefile

···
+# SPDX-License-Identifier: GPL-2.0
+CFLAGS = -O2 -Wall
+TEST_GEN_PROGS := tty_tstamp_update
+
+include ../lib.mk

tools/testing/selftests/tty/tty_tstamp_update.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <linux/limits.h>
+
+#include "../kselftest.h"
+
+#define MIN_TTY_PATH_LEN 8
+
+static bool tty_valid(char *tty)
+{
+	if (strlen(tty) < MIN_TTY_PATH_LEN)
+		return false;
+
+	if (strncmp(tty, "/dev/tty", MIN_TTY_PATH_LEN) == 0 ||
+	    strncmp(tty, "/dev/pts", MIN_TTY_PATH_LEN) == 0)
+		return true;
+
+	return false;
+}
+
+static int write_dev_tty(void)
+{
+	FILE *f;
+	int r = 0;
+
+	f = fopen("/dev/tty", "r+");
+	if (!f)
+		return -errno;
+
+	r = fprintf(f, "hello, world!\n");
+	if (r != strlen("hello, world!\n"))
+		r = -EIO;
+
+	fclose(f);
+	return r;
+}
+
+int main(int argc, char **argv)
+{
+	int r;
+	char tty[PATH_MAX] = {};
+	struct stat st1, st2;
+
+	ksft_print_header();
+	ksft_set_plan(1);
+
+	r = readlink("/proc/self/fd/0", tty, PATH_MAX);
+	if (r < 0)
+		ksft_exit_fail_msg("readlink on /proc/self/fd/0 failed: %m\n");
+
+	if (!tty_valid(tty))
+		ksft_exit_skip("invalid tty path '%s'\n", tty);
+
+	r = stat(tty, &st1);
+	if (r < 0)
+		ksft_exit_fail_msg("stat failed on tty path '%s': %m\n", tty);
+
+	/* We need to wait at least 8 seconds in order to observe timestamp change */
+	/* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fbf47635315ab308c9b58a1ea0906e711a9228de */
+	sleep(10);
+
+	r = write_dev_tty();
+	if (r < 0)
+		ksft_exit_fail_msg("failed to write to /dev/tty: %s\n",
+				   strerror(-r));
+
+	r = stat(tty, &st2);
+	if (r < 0)
+		ksft_exit_fail_msg("stat failed on tty path '%s': %m\n", tty);
+
+	/* We wrote to the terminal so timestamps should have been updated */
+	if (st1.st_atim.tv_sec == st2.st_atim.tv_sec &&
+	    st1.st_mtim.tv_sec == st2.st_mtim.tv_sec) {
+		ksft_test_result_fail("tty timestamps not updated\n");
+		ksft_exit_fail();
+	}
+
+	ksft_test_result_pass(
+		"timestamps of terminal '%s' updated after write to /dev/tty\n", tty);
+	return EXIT_SUCCESS;
+}