tape: add pmt bsf

src/bin/pmt.rs

@@ -96,6 +96,37 @@ fn get_tape_handle(param: &Value) -> Result<LinuxTapeHandle, Error> {
     bail!("no drive/device specified");
 }
 
+#[api(
+   input: {
+        properties: {
+            drive: {
+                schema: DRIVE_NAME_SCHEMA,
+                optional: true,
+            },
+            device: {
+                schema: LINUX_DRIVE_PATH_SCHEMA,
+                optional: true,
+            },
+            count: {
+                description: "File mark count.",
+                type: i32,
+                minimum: 1
+            },
+        },
+    },
+)]
+/// Backward space count files (position before file mark).
+///
+/// The tape is positioned on the last block of the previous file.
+fn bsf(count: i32, param: Value) -> Result<(), Error> {
+
+    let mut handle = get_tape_handle(&param)?;
+
+    handle.backward_space_count_files(count)?;
+
+    Ok(())
+}
+
 #[api(
    input: {
         properties: {
@@ -456,6 +487,7 @@ fn main() -> Result<(), Error> {
     };
 
     let cmd_def = CliCommandMap::new()
+        .insert("bsf", std_cmd(&API_METHOD_BSF))
         .insert("cartridge-memory", std_cmd(&API_METHOD_CARTRIDGE_MEMORY))
         .insert("eject", std_cmd(&API_METHOD_EJECT))
         .insert("eod", std_cmd(&API_METHOD_EOD))

src/tape/drive/linux_tape.rs

@@ -217,6 +217,19 @@ impl LinuxTapeHandle {
         Ok(())
     }
 
+    pub fn backward_space_count_files(&mut self, count: i32) -> Result<(), Error> {
+
+        let cmd = mtop { mt_op: MTCmd::MTBSF, mt_count: count, };
+
+        unsafe {
+            mtioctop(self.file.as_raw_fd(), &cmd)
+        }.map_err(|err| {
+            format_err!("backward space {} files failed - {}", count, err)
+        })?;
+
+        Ok(())
+    }
+
     /// Set tape compression feature
     pub fn set_compression(&self, on: bool) -> Result<(), Error> {