move luks2 check into own fn

src/luks.rs

@@ -34,13 +34,18 @@ impl LuksDevice {
         }
     }
 
+    fn require_luks2(&mut self) -> Fido2LuksResult<()> {
+        if !self.is_luks2()? {
+            return Err(LuksError::Luks2Required.into());
+        }
+        Ok(())
+    }
+
     pub fn tokens<'a>(
         &'a mut self,
     ) -> Fido2LuksResult<Box<dyn Iterator<Item = Fido2LuksResult<(u32, Fido2LuksToken)>> + 'a>>
     {
-        if !self.is_luks2()? {
-            return Err(LuksError::Luks2Required.into());
-        }
+        self.require_luks2()?;
         Ok(Box::new(
             (0..32)
                 .map(move |i| {
@@ -91,6 +96,7 @@ impl LuksDevice {
     }
 
     pub fn add_token(&mut self, data: &Fido2LuksToken) -> Fido2LuksResult<()> {
+        self.require_luks2()?;
         self.device
             .token_handle()
             .json_set(TokenInput::AddToken(&serde_json::to_value(&data).unwrap()))?;
@@ -98,6 +104,7 @@ impl LuksDevice {
     }
 
     pub fn remove_token(&mut self, token: u32) -> Fido2LuksResult<()> {
+        self.require_luks2()?;
         self.device
             .token_handle()
             .json_set(TokenInput::RemoveToken(token))?;
@@ -105,6 +112,7 @@ impl LuksDevice {
     }
 
     pub fn update_token(&mut self, token: u32, data: &Fido2LuksToken) -> Fido2LuksResult<()> {
+        self.require_luks2()?;
         self.device
             .token_handle()
             .json_set(TokenInput::ReplaceToken(