Make rootfs finalization repeatable

1 files changed, 18 insertions, 3 deletions

diff --git a/src/rootfs.rs b/src/rootfs.rs
index 06b2557..9246aa8 100644
--- a/src/rootfs.rs
+++ b/src/rootfs.rs
@@ -167,7 +167,7 @@ fn copy_entry(
         if let Some(parent) = output.parent() {
             fs::create_dir_all(parent)?;
         }
-        symlink(&target, &output).with_context(|| format!("create symlink {}", output.display()))?;
+        replace_with_symlink(&target, &output)?;
         manifest.record(destination);
     } else if metadata.file_type().is_file() {
         if let Some(parent) = output.parent() {
@@ -204,8 +204,23 @@ fn enable_service(rootfs: &Path, service: &ServiceName, manifest: &mut MutationM
     ))?;
     let output = rootfs.join(destination.as_path());
     fs::create_dir_all(output.parent().expect("service path has a parent"))?;
-    symlink(format!("/usr/lib/systemd/system/{}", service.0), &output)
-        .with_context(|| format!("enable service {}", service.0))?;
+    replace_with_symlink(
+        Path::new(&format!("/usr/lib/systemd/system/{}", service.0)),
+        &output,
+    )
+    .with_context(|| format!("enable service {}", service.0))?;
     manifest.record(destination.as_path());
     Ok(())
 }
+
+fn replace_with_symlink(target: &Path, output: &Path) -> Result<()> {
+    match fs::symlink_metadata(output) {
+        Ok(metadata) if metadata.file_type().is_dir() => {
+            bail!("cannot replace directory with symlink: {}", output.display());
+        }
+        Ok(_) => fs::remove_file(output).with_context(|| format!("replace {}", output.display()))?,
+        Err(error) if error.kind() == std::io::ErrorKind::NotFound => {}
+        Err(error) => return Err(error).with_context(|| format!("inspect {}", output.display())),
+    }
+    symlink(target, output).with_context(|| format!("create symlink {}", output.display()))
+}