selftests: tmpfs: Add kselftest support to tmpfs

Replace direct error handling with 'ksft_test_result_*'
macros for better reporting.

Test logs:

Before change:
- Without root
 error: unshare, errno 1

- With root
 No, output

After change:
- Without root
TAP version 13
1..1
ok 2 # SKIP This test needs root to run!
Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0

- With root
TAP version 13
1..1
ok 1 Test : Success
Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0

Link: https://lore.kernel.org/r/20250105085255.124929-3-cvam0000@gmail.com
Signed-off-by: Shivam Chaudhary <cvam0000@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: cvam0000

tools/testing/selftests/tmpfs/bug-link-o-tmpfile.c

@@ -41,39 +41,38 @@ int main(void)
 
 	if (unshare(CLONE_NEWNS) == -1) {
 		if (errno == ENOSYS || errno == EPERM) {
-			fprintf(stderr, "error: unshare, errno %d\n", errno);
-			return 4;
+			ksft_exit_skip("unshare() error: unshare, errno %d\n", errno);
+		} else {
+			ksft_exit_fail_msg("unshare() error: unshare, errno %d\n", errno);
 		}
-		fprintf(stderr, "error: unshare, errno %d\n", errno);
-		return 1;
 	}
+
 	if (mount(NULL, "/", NULL, MS_PRIVATE|MS_REC, NULL) == -1) {
-		fprintf(stderr, "error: mount '/', errno %d\n", errno);
-		return 1;
+		ksft_exit_fail_msg("mount() error: Root filesystem private mount: Fail %d\n", errno);
 	}
 
 	/* Our heroes: 1 root inode, 1 O_TMPFILE inode, 1 permanent inode. */
 	if (mount(NULL, "/tmp", "tmpfs", 0, "nr_inodes=3") == -1) {
-		fprintf(stderr, "error: mount tmpfs, errno %d\n", errno);
-		return 1;
+		ksft_exit_fail_msg("mount() error: Mounting tmpfs on /tmp: Fail %d\n", errno);
 	}
 
 	fd = openat(AT_FDCWD, "/tmp", O_WRONLY|O_TMPFILE, 0600);
 	if (fd == -1) {
-		fprintf(stderr, "error: open 1, errno %d\n", errno);
-		return 1;
+		ksft_exit_fail_msg("openat() error: Open first temporary file: Fail %d\n", errno);
 	}
+
 	if (linkat(fd, "", AT_FDCWD, "/tmp/1", AT_EMPTY_PATH) == -1) {
-		fprintf(stderr, "error: linkat, errno %d\n", errno);
-		return 1;
+		ksft_exit_fail_msg("linkat() error: Linking the temporary file: Fail %d\n", errno);
+		/* Ensure fd is closed on failure */
+		close(fd);
 	}
 	close(fd);
 
 	fd = openat(AT_FDCWD, "/tmp", O_WRONLY|O_TMPFILE, 0600);
 	if (fd == -1) {
-		fprintf(stderr, "error: open 2, errno %d\n", errno);
-		return 1;
+		ksft_exit_fail_msg("openat() error: Opening the second temporary file: Fail %d\n", errno);
 	}
-
+	ksft_test_result_pass(" ");
+	ksft_exit_pass();
 	return 0;
 }