tape: improve MediaChange trait

We expose the whole MtxStatus, and we can load/store from/to
specified slot numbers.

src/tape/changer/mod.rs

@@ -15,21 +15,52 @@ use anyhow::Error;
 /// Interface to media change devices
 pub trait MediaChange {
 
-    /// Load media into drive
+    /// Returns the changer status
+    fn status(&mut self) -> Result<MtxStatus, Error>;
+
+    /// Load media from storage slot into drive
+    fn load_media_from_slot(&mut self, slot: u64) -> Result<(), Error>;
+
+    /// Load media by changer-id into drive
     ///
     /// This unloads first if the drive is already loaded with another media.
+    ///
+    /// Note: This refuses to load media inside import/export slots.
     fn load_media(&mut self, changer_id: &str) -> Result<(), Error>;
 
     /// Unload media from drive
     ///
     /// This is a nop on drives without autoloader.
-    fn unload_media(&mut self) -> Result<(), Error>;
+    fn unload_media(&mut self, target_slot: Option<u64>) -> Result<(), Error>;
 
     /// Returns true if unload_media automatically ejects drive media
     fn eject_on_unload(&self) -> bool {
         false
     }
 
-    /// List media changer IDs (barcodes)
-    fn list_media_changer_ids(&self) -> Result<Vec<String>, Error>;
+    /// List online media changer IDs (barcodes)
+    ///
+    /// List acessible (online) changer IDs. This does not include
+    /// media inside import-export slots or cleaning media.
+    fn online_media_changer_ids(&mut self) -> Result<Vec<String>, Error> {
+        let status = self.status()?;
+
+        let mut list = Vec::new();
+
+        for drive_status in status.drives.iter() {
+            if let ElementStatus::VolumeTag(ref tag) = drive_status.status {
+                list.push(tag.clone());
+            }
+        }
+
+        for (import_export, element_status) in status.slots.iter() {
+            if *import_export { continue; }
+            if let ElementStatus::VolumeTag(ref tag) = element_status {
+                if !tag.starts_with("CLN") { continue; }
+                list.push(tag.clone());
+            }
+        }
+
+        Ok(list)
+    }
 }