tape: add tape read trait

src/tape/mod.rs

@@ -2,3 +2,6 @@ pub mod file_formats;
 
 mod tape_write;
 pub use tape_write::*;
+
+mod tape_read;
+pub use tape_read::*;

src/tape/tape_read.rs

@@ -0,0 +1,45 @@
+use std::io::Read;
+
+/// Read trait for tape devices
+///
+/// Normal Read, but allows to query additional status flags.
+pub trait TapeRead: Read {
+    /// Return true if there is an "INCOMPLETE" mark at EOF
+    ///
+    /// Raises an error if you query this flag before reaching EOF.
+    fn is_incomplete(&self) -> Result<bool, std::io::Error>;
+
+    /// Return true if there is a file end marker before EOF
+    ///
+    /// Raises an error if you query this flag before reaching EOF.
+    fn has_end_marker(&self) -> Result<bool, std::io::Error>;
+}
+
+/// Read a single block from a tape device
+///
+/// Assumes that 'reader' is a linux tape device.
+///
+/// Return true on success, false on EOD
+pub fn tape_device_read_block<R: Read>(
+    reader: &mut R,
+    buffer: &mut [u8],
+) -> Result<bool, std::io::Error> {
+
+    loop {
+        match reader.read(buffer) {
+            Ok(0) => { return Ok(false); /* EOD */ }
+            Ok(count) => {
+                if count == buffer.len() {
+                    return Ok(true);
+                }
+                proxmox::io_bail!("short block read ({} < {}). Tape drive uses wrong block size.",
+                                  count, buffer.len());
+            }
+            // handle interrupted system call
+            Err(err) if err.kind() == std::io::ErrorKind::Interrupted => {
+                continue;
+            }
+            Err(err) => return Err(err),
+        }
+    }
+}