tape: use LOCATE(16) SCSI command

Turns out this works on LTO4 and newer.

src/tape/drive/lto/mod.rs

@@ -215,31 +215,8 @@ impl LtoTapeHandle {
     }
 
     /// Position the tape after filemark count. Count 0 means BOT.
-    ///
-    /// Note: we dont use LOCATE(10), because that needs LTO5
     pub fn locate_file(&mut self, position: u64) ->  Result<(), Error> {
-
+        self.sg_tape.locate_file(position)
-        if position == 0 {
-            return self.rewind();
-        }
-
-        let current_position = self.current_file_number()?;
-
-        if current_position == position {
-            // make sure we are immediated afer the filemark
-            self.sg_tape.space_filemarks(-1)?;
-            self.sg_tape.space_filemarks(1)?;
-        } else if current_position < position {
-            let diff = position - current_position;
-            self.sg_tape.space_filemarks(diff.try_into()?)?;
-        } else {
-            let diff = current_position - position + 1;
-            self.sg_tape.space_filemarks(-diff.try_into()?)?;
-            // move to EOT side of filemark
-            self.sg_tape.space_filemarks(1)?;
-        }
-
-        Ok(())
     }
 
     pub fn erase_media(&mut self, fast: bool) -> Result<(), Error> {

src/tape/drive/lto/sg_tape.rs

@@ -295,6 +295,32 @@ impl SgTape {
         Ok(())
     }
 
+    pub fn locate_file(&mut self, position: u64) ->  Result<(), Error> {
+        if position == 0 {
+            return self.rewind();
+        }
+
+        let mut sg_raw = SgRaw::new(&mut self.file, 16)?;
+        sg_raw.set_timeout(Self::SCSI_TAPE_DEFAULT_TIMEOUT);
+        let mut cmd = Vec::new();
+        // Note: LOCATE(16) works for LTO4 or newer
+        cmd.extend(&[0x92, 0b000_01_000, 0, 0]); // LOCATE(16) filemarks
+        cmd.extend(&position.to_be_bytes());
+        cmd.extend(&[0, 0, 0, 0]);
+
+        sg_raw.do_command(&cmd)
+            .map_err(|err| format_err!("locate file {} failed - {}", position, err))?;
+
+        // move to other side of filemark
+        cmd.truncate(0);
+        cmd.extend(&[0x11, 0x01, 0, 0, 1, 0]); // SPACE(6) one filemarks
+
+        sg_raw.do_command(&cmd)
+            .map_err(|err| format_err!("locate file {} (space) failed - {}", position, err))?;
+
+        Ok(())
+    }
+
     pub fn position(&mut self) -> Result<ReadPositionLongPage, Error> {
 
         let expected_size = std::mem::size_of::<ReadPositionLongPage>();