Unmount disks on MacOS before writing

nix/cross-helpers.nix

@@ -85,7 +85,9 @@ in rec {
 
       crossParams = if host == target then {
         cc = pkgs.stdenv.cc;
-        extraBuildEnv = { };
+        extraBuildEnv = { 
+          RUST_SRC_PATH = "${pkgs.rust.packages.stable.rustPlatform.rustLibSrc}";
+        };
       } else rec {
         cc = pkgsCross.stdenv.cc;
         extraBuildEnv = {

src/writer_process/ipc.rs

@@ -49,6 +49,7 @@ pub enum ErrorType {
     VerificationFailed,
     UnexpectedTermination,
     UnknownChildProcError(String),
+    FailedToUnmount { message: String, exit_code: i32 },
 }
 
 impl From<std::io::Error> for ErrorType {
@@ -75,6 +76,10 @@ impl Display for ErrorType {
             ErrorType::UnknownChildProcError(err) => {
                 write!(f, "Unknown error occurred in child process: {err}")
             }
+            ErrorType::FailedToUnmount { message, exit_code } => write!(
+                f,
+                "Failed to unmount disk (exit code {exit_code})\n{message}"
+            ),
         }
     }
 }

src/writer_process/mod.rs

@@ -3,14 +3,16 @@
 //! IT IS NOT TO BE USED DIRECTLY BY THE USER! ITS API HAS NO STABILITY GUARANTEES!
 
 use std::fs::OpenOptions;
+use std::os::unix::process::ExitStatusExt;
+use std::process::{Command, Stdio};
 use std::{
     fs::File,
     io::{self, Read, Seek, Write},
 };
 
 use aligned_vec::avec_rt;
 use interprocess::local_socket::{prelude::*, GenericFilePath};
-use tracing::info;
+use tracing::{debug, info};
 use tracing_unwrap::ResultExt;
 
 use crate::childproc_common::child_init;
@@ -60,6 +62,36 @@ pub fn main() {
 }
 
 fn run(mut tx: impl FnMut(StatusMessage), args: &WriterProcessConfig) -> Result<(), ErrorType> {
+    if cfg!(target_os = "macos") && args.target_type == device::Type::Disk {
+        let mut command = Command::new("diskutil");
+        command
+            .arg("unmountdisk")
+            .arg(&args.dest)
+            .stdin(Stdio::null())
+            .stdout(Stdio::piped())
+            .stderr(Stdio::piped());
+
+        info!(?command, "spawning process to unmount disk");
+        let mut child = command.spawn()?;
+        debug!("successfully ran diskutil, waiting on child process");
+
+        let exit = child.wait()?;
+        let mut stderr = String::new();
+        child.stderr.take().unwrap().read_to_string(&mut stderr)?;
+        let mut stdout = String::new();
+        child.stdout.take().unwrap().read_to_string(&mut stdout)?;
+
+        debug!(?exit, ?stderr, "child exited");
+
+        let exit_code = exit.into_raw();
+        if !exit.success() {
+            return Err(ErrorType::FailedToUnmount {
+                message: format!("stderr: {stderr}\nstdout: {stdout}"),
+                exit_code,
+            });
+        }
+    }
+
     info!("Opening file {}", args.src.to_string_lossy());
     let mut file = File::open(&args.src).unwrap_or_log();
     let size = file.seek(io::SeekFrom::End(0))?;