bin: implement led revert

Command:

    $ vtcol leds set --revert

Implementing this detail of KDSETLED:

    [I]f a higher order bit is set, the LEDs revert to normal:
    displaying the state of the keyboard functions of caps lock, num
    lock, and scroll lock.

2 files changed, 26 insertions, 7 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 6193277..0669b87 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -186,6 +186,9 @@ impl KbLedState
     }
 
     #[inline]
+    pub fn revert(con: &Console) -> io::Result<()> { ioctl::kdsetled(con, None) }
+
+    #[inline]
     pub fn cap(&self) -> bool { (self.0 & 0x4) != 0 }
 
     #[inline]
diff --git a/src/vtcol.rs b/src/vtcol.rs
index 2fdec10..738a622 100644
--- a/src/vtcol.rs
+++ b/src/vtcol.rs
@@ -23,8 +23,8 @@ enum LedJob
 {
     /** Get keyboard LED state. */
     Get(bool),
-    /** Set keyboard LED state. */
-    Set(KbLedState),
+    /** Set keyboard LED state; ``None`` indicates revert. */
+    Set(Option<KbLedState>),
 }
 
 #[derive(Debug)]
@@ -230,8 +230,16 @@ impl<'a> Job
                                     .long("u8")
                                     .help("provide desired state as integer")
                                     .takes_value(true)
-                                    .required(true)
+                                    .required_unless_one(&["revert"])
                                     .value_name("STATE"),
+                            )
+                            .arg(
+                                Arg::with_name("revert")
+                                    .short("r")
+                                    .long("revert")
+                                    .help("revert LED state to normal")
+                                    .takes_value(false)
+                                    .conflicts_with("u8"),
                             ),
                     ),
             );
@@ -349,9 +357,12 @@ impl<'a> Job
                         Ok(Self::Leds(LedJob::Get(raw)))
                     },
                     ("set", Some(subm)) => {
+                        if subm.is_present("revert") {
+                            return Ok(Self::Leds(LedJob::Set(None)));
+                        }
                         let st: u8 = subm.value_of("u8").unwrap().parse()?;
                         let st = KbLedState::try_from(st)?;
-                        Ok(Self::Leds(LedJob::Set(st)))
+                        Ok(Self::Leds(LedJob::Set(Some(st))))
                     },
                     (junk, _) =>
                         Err(anyhow!(
@@ -525,13 +536,18 @@ impl<'a> Job
     }
 
     /** Set the keyboard LED state. */
-    fn set_leds(st: KbLedState) -> Result<()>
+    fn set_leds(st: Option<KbLedState>) -> Result<()>
     {
         let fd = Console::current()?;
         vrb!("console fd: {}", fd);
 
-        st.set(&fd)?;
-        vrb!("applied");
+        if let Some(st) = st {
+            st.set(&fd)?;
+            vrb!("applied");
+        } else {
+            KbLedState::revert(&fd)?;
+            vrb!("reverted");
+        }
 
         Ok(())
     }