More documentation!

Signed-off-by: Levente Kurusa <lkurusa@acm.org>

src/freezer.rs

@@ -1,18 +1,33 @@
-/* Freezer controller */
+//! This module contains the implementation of the `freezer` cgroup subsystem.
+//! 
+//! See the Kernel's documentation for more information about this subsystem, found at:
+//!  [Documentation/cgroup-v1/freezer-subsystem.txt](https://www.kernel.org/doc/Documentation/cgroup-v1/freezer-subsystem.txt)
 use std::path::PathBuf;
 use std::io::{Read, Write};
 
 use {Controllers, Controller, Resources, ControllIdentifier, Subsystem};
 
+/// A controller that allows controlling the `freezer` subsystem of a Cgroup.
+///
+/// In essence, this subsystem allows the user to freeze and thaw (== "un-freeze") the processes in
+/// the control group. This is done _transparently_ so that neither the parent, nor the children of
+/// the processes can observe the freeze.
+///
+/// Note that if the control group is currently in the `Frozen` or `Freezing` state, then no
+/// processes can be added to it.
 #[derive(Debug, Clone)]
 pub struct FreezerController{
     base: PathBuf,
     path: PathBuf,
 }
 
+/// The current state of the control group
 pub enum FreezerState {
+    /// The processes in the control group are _not_ frozen.
     Thawed,
+    /// The processes in the control group are in the processes of being frozen.
     Freezing,
+    /// The processes in the control group are frozen.
     Frozen,
 }
 
@@ -47,6 +62,7 @@ impl<'a> From<&'a Subsystem> for &'a FreezerController {
 }
 
 impl FreezerController {
+    /// Contructs a new `FreezerController` with `oroot` serving as the root of the control group.
     pub fn new(oroot: PathBuf) -> Self {
         let mut root = oroot;
         root.push(Self::controller_type().to_string());
@@ -55,18 +71,22 @@ impl FreezerController {
             path: root,
         }
     }
+
+    /// Freezes the processes in the control group.
     pub fn freeze(self: &Self) {
         self.open_path("freezer.state", true).and_then(|mut file| {
             file.write_all("FROZEN".to_string().as_ref()).ok()
         });
     }
 
+    /// Thaws, that is, unfreezes the processes in the control group.
     pub fn thaw(self: &Self) {
         self.open_path("freezer.state", true).and_then(|mut file| {
             file.write_all("THAWED".to_string().as_ref()).ok()
         });
     }
 
+    /// Retrieve the state of processes in the control group.
     pub fn state(self: &Self) -> FreezerState {
         self.open_path("freezer.state", false).and_then(|mut file| {
             let mut s = String::new();