Unmount apfs volumes before deleting them (#662)

src/action/macos/create_apfs_volume.rs

@@ -1,3 +1,4 @@
+use std::io::Cursor;
 use std::path::{Path, PathBuf};
 
 use tokio::process::Command;
@@ -7,7 +8,7 @@ use crate::action::{ActionError, ActionTag, StatefulAction};
 use crate::execute_command;
 
 use crate::action::{Action, ActionDescription};
-use crate::os::darwin::DiskUtilApfsListOutput;
+use crate::os::darwin::{DiskUtilApfsListOutput, DiskUtilInfoOutput};
 
 #[derive(Debug, serde::Deserialize, serde::Serialize, Clone)]
 pub struct CreateApfsVolume {
@@ -122,6 +123,38 @@ impl Action for CreateApfsVolume {
 
     #[tracing::instrument(level = "debug", skip_all)]
     async fn revert(&mut self) -> Result<(), ActionError> {
+        let currently_mounted = {
+            let buf = execute_command(
+                Command::new("/usr/sbin/diskutil")
+                    .process_group(0)
+                    .args(["info", "-plist"])
+                    .arg(&self.name)
+                    .stdin(std::process::Stdio::null()),
+            )
+            .await
+            .map_err(Self::error)?
+            .stdout;
+            let the_plist: DiskUtilInfoOutput =
+                plist::from_reader(Cursor::new(buf)).map_err(Self::error)?;
+
+            the_plist.mount_point.is_some()
+        };
+
+        // Unmounts the volume before attempting to remove it, avoiding 'in use' errors
+        // https://github.com/DeterminateSystems/nix-installer/issues/647
+        if !currently_mounted {
+            execute_command(
+                Command::new("/usr/sbin/diskutil")
+                    .process_group(0)
+                    .args(["unmount", "force", &self.name])
+                    .stdin(std::process::Stdio::null()),
+            )
+            .await
+            .map_err(Self::error)?;
+        } else {
+            tracing::debug!("Volume was already unmounted, can skip unmounting")
+        }
+
         execute_command(
             Command::new("/usr/sbin/diskutil")
                 .process_group(0)