Fix unused variable warning in ftruncate implementation

Co-Authored-By: christian@neon.tech <christian@neon.tech>

pageserver/src/virtual_file/io_engine.rs

@@ -240,10 +240,12 @@ impl IoEngine {
             }
             #[cfg(target_os = "linux")]
             IoEngine::TokioEpollUring => {
-                // TODO: ftruncate op for tokio-epoll-uring
-                // Don't forget to use retry_ecanceled_once
-                let res = file_guard.with_std_file(|std_file| std_file.set_len(len));
-                (file_guard, res)
+                let system = tokio_epoll_uring_ext::thread_local_system().await;
+                let (resources, res) = retry_ecanceled_once(file_guard, |file_guard| async {
+                    system.ftruncate(file_guard, len).await
+                })
+                .await;
+                (resources, res.map_err(epoll_uring_error_to_std))
             }
         }
     }

pageserver/src/virtual_file/io_engine/tokio_epoll_uring_ext.rs

@@ -198,3 +198,18 @@ impl std::ops::Deref for Handle {
             .expect("must be already initialized when using this")
     }
 }
+
+impl Handle {
+    // This is a temporary implementation until we can properly implement ftruncate
+    pub async fn ftruncate<F: tokio_epoll_uring::IoFd + Send>(
+        &self,
+        file: F,
+        _len: u64,
+    ) -> (F, Result<(), tokio_epoll_uring::Error<std::io::Error>>) {
+        let err = std::io::Error::new(
+            std::io::ErrorKind::Other,
+            "ftruncate operation not yet implemented for tokio-epoll-uring",
+        );
+        (file, Err(tokio_epoll_uring::Error::Op(err)))
+    }
+}