feat(tvix/store/fuse): allow listing

This provides an additional configuration flag to the tvix-store mount
subcommand, and logic in the fuse module to request listing for the
root of the mountpoint.

Change-Id: I05a8bc11f7991b574696f27a30afe0f4e718a58c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9217
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: adisbladis <adisbladis@gmail.com>
Tested-by: BuildkiteCI

tvix/store/src/fuse/tests.rs

@@ -25,6 +25,17 @@ fn setup_and_mount<P: AsRef<Path>, F>(
     mountpoint: P,
     setup_fn: F,
 ) -> Result<fuser::BackgroundSession, std::io::Error>
+where
+    F: Fn(Arc<dyn BlobService>, Arc<dyn DirectoryService>, Arc<dyn PathInfoService>),
+{
+    setup_and_mount_with_listing(mountpoint, setup_fn, false)
+}
+
+fn setup_and_mount_with_listing<P: AsRef<Path>, F>(
+    mountpoint: P,
+    setup_fn: F,
+    list_root: bool,
+) -> Result<fuser::BackgroundSession, std::io::Error>
 where
     F: Fn(Arc<dyn BlobService>, Arc<dyn DirectoryService>, Arc<dyn PathInfoService>),
 {
@@ -38,7 +49,12 @@ where
         path_info_service.clone(),
     );
 
-    let fs = FUSE::new(blob_service, directory_service, path_info_service);
+    let fs = FUSE::new(
+        blob_service,
+        directory_service,
+        path_info_service,
+        list_root,
+    );
     fuser::spawn_mount2(fs, mountpoint, &[])
 }
 
@@ -280,6 +296,34 @@ fn root() {
     fuser_session.join()
 }
 
+/// Ensure listing the root is allowed if configured explicitly
+#[test]
+fn root_with_listing() {
+    // https://plume.benboeckel.net/~/JustAnotherBlog/skipping-tests-in-rust
+    if !std::path::Path::new("/dev/fuse").exists() {
+        eprintln!("skipping test");
+        return;
+    }
+    let tmpdir = TempDir::new().unwrap();
+
+    let fuser_session =
+        setup_and_mount_with_listing(tmpdir.path(), populate_blob_a, true).expect("must succeed");
+
+    {
+        // read_dir succeeds, but getting the first element will fail.
+        let mut it = fs::read_dir(tmpdir).expect("must succeed");
+
+        let e = it.next().expect("must be some").expect("must succeed");
+
+        let metadata = e.metadata().expect("must succeed");
+        assert!(metadata.is_file());
+        assert!(metadata.permissions().readonly());
+        assert_eq!(fixtures::BLOB_A.len() as u64, metadata.len());
+    }
+
+    fuser_session.join()
+}
+
 /// Ensure we can stat a file at the root
 #[test]
 fn stat_file_at_root() {