Fail if failed to ummount the filesystems

src/error.rs

@@ -55,6 +55,9 @@ pub enum ErrorKind {
 
     #[fail(display = "Error caused by the interactive mode")]
     Interactive,
+
+    #[fail(display = "Failed umounting filesystems")]
+    UmountFailure,
 }
 
 impl Fail for Error {

src/main.rs

@@ -210,6 +210,10 @@ fn create(command: CreateCommand) -> Result<(), Error> {
     }
 
     info!("Unmounting filesystems");
+    mount_stack.umount()?;
+
+    info!("Installation succeeded. It is now safe to unplug your device.");
+
     Ok(())
 }
 

src/mountstack.rs

@@ -1,3 +1,5 @@
+use super::error::{Error, ErrorKind};
+use failure::Fail;
 use log::{debug, warn};
 use nix;
 use nix::mount::{mount, umount, MsFlags};
@@ -48,15 +50,24 @@ impl<'a> MountStack<'a> {
         self.targets.push(target);
         Ok(())
     }
-}
 
-impl<'a> Drop for MountStack<'a> {
-    fn drop(&mut self) {
+    pub fn umount(&mut self) -> Result<(), Error> {
+        let mut result = Ok(());
+
         while let Some(target) = self.targets.pop() {
             debug!("Unmounting {}", target.display());
-            if !umount(target).is_ok() {
-                warn!("Unable to umount {}", target.display());
+            if let Err(e) = umount(target) {
+                warn!("Unable to umount {}: {}", target.display(), e);
+                result = Err(Error::from(e.context(ErrorKind::UmountFailure)));
             };
         }
+
+        result
+    }
+}
+
+impl<'a> Drop for MountStack<'a> {
+    fn drop(&mut self) {
+        self.umount().ok();
     }
 }