tape: make fsf/bsf driver specific

Because the virtual tape driver behaves different than LTO drives.

src/tape/drive/lto/mod.rs

@@ -179,6 +179,14 @@ impl LtoTapeHandle {
         Ok(status)
     }
 
+    pub fn forward_space_count_files(&mut self, count: usize) -> Result<(), Error> {
+        self.sg_tape.space_filemarks(isize::try_from(count)?)
+    }
+
+    pub fn backward_space_count_files(&mut self, count: usize) -> Result<(), Error> {
+        self.sg_tape.space_filemarks(-isize::try_from(count)?)
+    }
+
     pub fn erase_media(&mut self, fast: bool) -> Result<(), Error> {
         self.sg_tape.erase_media(fast)
     }
@@ -211,12 +219,25 @@ impl TapeDriver for LtoTapeHandle {
         self.sg_tape.move_to_eom()
     }
 
-    fn forward_space_count_files(&mut self, count: usize) -> Result<(), Error> {
+    fn move_to_last_file(&mut self) -> Result<(), Error> {
-        self.sg_tape.space_filemarks(isize::try_from(count)?)
-    }
 
-    fn backward_space_count_files(&mut self, count: usize) -> Result<(), Error> {
+        self.move_to_eom()?;
-        self.sg_tape.space_filemarks(-isize::try_from(count)?)
+
+        let pos = self.current_file_number()?;
+
+        if pos == 0 {
+            bail!("move_to_last_file failed - media contains no data");
+        }
+
+        if pos == 1 {
+            self.rewind()?;
+            return Ok(());
+        }
+
+        self.backward_space_count_files(2)?;
+        self.forward_space_count_files(1)?;
+
+        Ok(())
     }
 
     fn rewind(&mut self) -> Result<(), Error> {

src/tape/drive/mod.rs

@@ -88,24 +88,7 @@ pub trait TapeDriver {
     fn move_to_eom(&mut self) -> Result<(), Error>;
 
     /// Move to last file
-    fn move_to_last_file(&mut self) -> Result<(), Error> {
+    fn move_to_last_file(&mut self) -> Result<(), Error>;
-
-        self.move_to_eom()?;
-
-        if self.current_file_number()? == 0 {
-            bail!("move_to_last_file failed - media contains no data");
-        }
-
-        self.backward_space_count_files(2)?;
-
-        Ok(())
-    }
-
-    /// Forward space count files. The tape is positioned on the first block of the next file.
-    fn forward_space_count_files(&mut self, count: usize) -> Result<(), Error>;
-
-    /// Backward space count files.  The tape is positioned on the last block of the previous file.
-    fn backward_space_count_files(&mut self, count: usize) -> Result<(), Error>;
 
     /// Current file number
     fn current_file_number(&mut self) -> Result<u64, Error>;

src/tape/drive/virtual_tape.rs

@@ -181,6 +181,53 @@ impl VirtualTapeHandle {
         Ok(list)
     }
 
+    #[allow(dead_code)]
+    fn forward_space_count_files(&mut self, count: usize) -> Result<(), Error> {
+        let mut status = self.load_status()?;
+        match status.current_tape {
+            Some(VirtualTapeStatus { ref name, ref mut pos }) => {
+
+                let index = self.load_tape_index(name)
+                    .map_err(|err| io::Error::new(io::ErrorKind::Other, err.to_string()))?;
+
+                let new_pos = *pos + count;
+                if new_pos <= index.files {
+                    *pos = new_pos;
+                } else {
+                    bail!("forward_space_count_files failed: move beyond EOT");
+                }
+
+                self.store_status(&status)
+                    .map_err(|err| io::Error::new(io::ErrorKind::Other, err.to_string()))?;
+
+                Ok(())
+            }
+            None => bail!("drive is empty (no tape loaded)."),
+        }
+    }
+
+    // Note: behavior differs from LTO, because we always position at
+    // EOT side.
+    fn backward_space_count_files(&mut self, count: usize) -> Result<(), Error> {
+        let mut status = self.load_status()?;
+        match status.current_tape {
+            Some(VirtualTapeStatus { ref mut pos, .. }) => {
+
+                if count <= *pos {
+                    *pos = *pos - count;
+                } else {
+                    bail!("backward_space_count_files failed: move before BOT");
+                }
+
+                self.store_status(&status)
+                    .map_err(|err| io::Error::new(io::ErrorKind::Other, err.to_string()))?;
+
+                Ok(())
+            }
+            None => bail!("drive is empty (no tape loaded)."),
+        }
+    }
+
 }
 
 impl TapeDriver for VirtualTapeHandle {
@@ -199,6 +246,21 @@ impl TapeDriver for VirtualTapeHandle {
         }
     }
 
+    /// Move to last file
+    fn move_to_last_file(&mut self) -> Result<(), Error> {
+
+        self.move_to_eom()?;
+
+        if self.current_file_number()? == 0 {
+            bail!("move_to_last_file failed - media contains no data");
+        }
+
+        self.backward_space_count_files(1)?;
+
+        Ok(())
+    }
+
+
     fn read_next_file(&mut self) -> Result<Option<Box<dyn TapeRead>>, io::Error> {
         let mut status = self.load_status()
             .map_err(|err| io::Error::new(io::ErrorKind::Other, err.to_string()))?;
@@ -304,50 +366,6 @@ impl TapeDriver for VirtualTapeHandle {
         }
     }
 
-    fn forward_space_count_files(&mut self, count: usize) -> Result<(), Error> {
-        let mut status = self.load_status()?;
-        match status.current_tape {
-            Some(VirtualTapeStatus { ref name, ref mut pos }) => {
-
-                let index = self.load_tape_index(name)
-                    .map_err(|err| io::Error::new(io::ErrorKind::Other, err.to_string()))?;
-
-                let new_pos = *pos + count;
-                if new_pos <= index.files {
-                    *pos = new_pos;
-                } else {
-                    bail!("forward_space_count_files failed: move beyond EOT");
-                }
-
-                self.store_status(&status)
-                    .map_err(|err| io::Error::new(io::ErrorKind::Other, err.to_string()))?;
-
-                Ok(())
-            }
-            None => bail!("drive is empty (no tape loaded)."),
-        }
-    }
-
-    fn backward_space_count_files(&mut self, count: usize) -> Result<(), Error> {
-        let mut status = self.load_status()?;
-        match status.current_tape {
-            Some(VirtualTapeStatus { ref mut pos, .. }) => {
-
-                if count <= *pos {
-                    *pos = *pos - count;
-                } else {
-                    bail!("backward_space_count_files failed: move before BOT");
-                }
-
-                self.store_status(&status)
-                    .map_err(|err| io::Error::new(io::ErrorKind::Other, err.to_string()))?;
-
-                Ok(())
-            }
-            None => bail!("drive is empty (no tape loaded)."),
-        }
-    }
-
     fn rewind(&mut self) -> Result<(), Error> {
         let mut status = self.load_status()?;
         match status.current_tape {