node: Put NodeType <-> dev_t conversions closer together

Group all this logic together in functions inside `impl NodeType`.

src/node/mod.rs

@@ -44,16 +44,7 @@ impl DrmNode {
             return Err(CreateDrmNodeError::NotDrmNode);
         }
 
-        // The type of the DRM node is determined by the minor number ranges:
-        //   0 -  63 -> Primary
-        //  64 - 127 -> Control
-        // 128 - 255 -> Render
-        let ty = match minor(dev) >> 6 {
-            0 => NodeType::Primary,
-            1 => NodeType::Control,
-            2 => NodeType::Render,
-            _ => return Err(CreateDrmNodeError::NotDrmNode),
-        };
+        let ty = NodeType::from_dev_id(dev)?;
 
         Ok(DrmNode { dev, ty })
     }
@@ -151,14 +142,32 @@ impl NodeType {
         }
     }
 
+    pub fn from_dev_id(dev: dev_t) -> Result<Self, CreateDrmNodeError> {
+        // The type of the DRM node is determined by the minor number ranges:
+        //   0 -  63 -> Primary
+        //  64 - 127 -> Control
+        // 128 - 255 -> Render
+        Ok(match minor(dev) >> 6 {
+            0 => Self::Primary,
+            1 => Self::Control,
+            2 => Self::Render,
+            _ => return Err(CreateDrmNodeError::NotDrmNode),
+        })
+    }
+
     #[cfg(not(target_os = "linux"))]
-    fn minor_base(&self) -> u32 {
+    fn minor_index(&self) -> u32 {
         match self {
             NodeType::Primary => 0,
-            NodeType::Control => 64,
-            NodeType::Render => 128,
+            NodeType::Control => 1,
+            NodeType::Render => 2,
         }
     }
+
+    #[cfg(not(target_os = "linux"))]
+    fn minor_base(&self) -> u32 {
+        self.minor_index() << 6
+    }
 }
 
 impl Display for NodeType {