fsfreeze: Add tool

Add fsfreeze, a Linux-specific tool used to freeze/thaw writes to a
filesystem. It's an extremely simple tool so this should have full
feature-parity.

tests/by-util/test_fsfreeze.rs

@@ -0,0 +1,62 @@
+// This file is part of the uutils util-linux package.
+//
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+
+use crate::common::util::TestScenario;
+
+#[test]
+fn test_invalid_arg() {
+    new_ucmd!().arg("--definitely-invalid").fails().code_is(1);
+}
+
+#[test]
+fn test_operations_mutually_exclusive() {
+    new_ucmd!()
+        .arg("--freeze")
+        .arg("--unfreeze")
+        .arg("/foo")
+        .fails()
+        .code_is(1)
+        .stderr_contains("the argument '--freeze' cannot be used with '--unfreeze'");
+}
+
+#[cfg(target_os = "linux")]
+mod linux {
+    use crate::common::util::TestScenario;
+
+    #[test]
+    fn test_fails_on_non_existing_path() {
+        new_ucmd!()
+            .arg("--unfreeze")
+            .arg("/non/existing")
+            .fails()
+            .code_is(1)
+            .stderr_contains("No such file or directory");
+    }
+
+    #[test]
+    fn test_fails_on_non_directory() {
+        new_ucmd!()
+            .arg("--unfreeze")
+            .arg("/dev/null")
+            .fails()
+            .code_is(1)
+            .stderr_contains("not a directory");
+    }
+}
+
+#[cfg(not(target_os = "linux"))]
+mod non_linux {
+    use crate::common::util::TestScenario;
+
+    #[test]
+    fn test_fails_on_unsupported_platforms() {
+        new_ucmd!()
+            .arg("--unfreeze")
+            .arg("/non/existing")
+            .fails()
+            .code_is(1)
+            .stderr_is("fsfreeze: `fsfreeze` is available only on Linux.\n");
+    }
+}

tests/tests.rs

@@ -36,3 +36,7 @@ mod test_last;
 #[cfg(feature = "dmesg")]
 #[path = "by-util/test_dmesg.rs"]
 mod test_dmesg;
+
+#[cfg(feature = "fsfreeze")]
+#[path = "by-util/test_fsfreeze.rs"]
+mod test_fsfreeze;