feat(tvix/store/fuse): initial implementation

This is a first implementation of a FUSE filesystem, mounting tvix-store
to a given location.

This is mostly meant as one additional lens into a store, and could be
used for builds. It's not meant to be used as a general-purpose thing.

It still has some rough edges:

 - It doesn't implement open/close, so it doesn't use file handles.
   Which means, we need to open blobs for partial reads over and over
   again.
 - It doesn't implement seek, as BlobReader doesn't implement seek yet.
 - It doesn't track "lifetimes" of inodes by listening on forget,
   meaning it might hold more data in memory than necessary.
 - As we don't have store composition (and a caching layer) yet,
   operations might be slow.

Change-Id: Ib1812ed761dfaf6aeb548443ae939c87530b7be8
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8667
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/store/src/fuse/tests.rs

@@ -0,0 +1,797 @@
+use std::fs;
+use std::io::Cursor;
+use std::os::unix::prelude::MetadataExt;
+use std::path::Path;
+use std::sync::Arc;
+
+use tempfile::TempDir;
+
+use crate::blobservice::BlobService;
+use crate::directoryservice::DirectoryService;
+use crate::pathinfoservice::PathInfoService;
+use crate::proto::{DirectoryNode, FileNode, PathInfo};
+use crate::tests::fixtures;
+use crate::tests::utils::{gen_blob_service, gen_directory_service, gen_pathinfo_service};
+use crate::{proto, FUSE};
+
+const BLOB_A_NAME: &str = "00000000000000000000000000000000-test";
+const SYMLINK_NAME: &str = "11111111111111111111111111111111-test";
+const SYMLINK_NAME2: &str = "44444444444444444444444444444444-test";
+const DIRECTORY_WITH_KEEP_NAME: &str = "22222222222222222222222222222222-test";
+const DIRECTORY_COMPLICATED_NAME: &str = "33333333333333333333333333333333-test";
+
+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>),
+{
+    let blob_service = gen_blob_service();
+    let directory_service = gen_directory_service();
+    let path_info_service = gen_pathinfo_service(blob_service.clone(), directory_service.clone());
+
+    setup_fn(
+        blob_service.clone(),
+        directory_service.clone(),
+        path_info_service.clone(),
+    );
+
+    let fs = FUSE::new(blob_service, directory_service, path_info_service);
+    fuser::spawn_mount2(fs, mountpoint, &[])
+}
+
+fn populate_blob_a(
+    blob_service: Arc<dyn BlobService>,
+    _directory_service: Arc<dyn DirectoryService>,
+    path_info_service: Arc<dyn PathInfoService>,
+) {
+    // Upload BLOB_A
+    let mut bw = blob_service.open_write();
+    std::io::copy(&mut Cursor::new(fixtures::BLOB_A.to_vec()), &mut bw)
+        .expect("must succeed uploading");
+    bw.close().expect("must succeed closing");
+
+    // Create a PathInfo for it
+    let path_info = PathInfo {
+        node: Some(proto::Node {
+            node: Some(proto::node::Node::File(FileNode {
+                name: BLOB_A_NAME.to_string(),
+                digest: fixtures::BLOB_A_DIGEST.to_vec(),
+                size: fixtures::BLOB_A.len() as u32,
+                executable: false,
+            })),
+        }),
+        ..Default::default()
+    };
+    path_info_service.put(path_info).expect("must succeed");
+}
+
+fn populate_symlink(
+    _blob_service: Arc<dyn BlobService>,
+    _directory_service: Arc<dyn DirectoryService>,
+    path_info_service: Arc<dyn PathInfoService>,
+) {
+    // Create a PathInfo for it
+    let path_info = PathInfo {
+        node: Some(proto::Node {
+            node: Some(proto::node::Node::Symlink(proto::SymlinkNode {
+                name: SYMLINK_NAME.to_string(),
+                target: BLOB_A_NAME.to_string(),
+            })),
+        }),
+        ..Default::default()
+    };
+    path_info_service.put(path_info).expect("must succeed");
+}
+
+/// This writes a symlink pointing to /nix/store/somewhereelse,
+/// which is the same symlink target as "aa" inside DIRECTORY_COMPLICATED.
+fn populate_symlink2(
+    _blob_service: Arc<dyn BlobService>,
+    _directory_service: Arc<dyn DirectoryService>,
+    path_info_service: Arc<dyn PathInfoService>,
+) {
+    // Create a PathInfo for it
+    let path_info = PathInfo {
+        node: Some(proto::Node {
+            node: Some(proto::node::Node::Symlink(proto::SymlinkNode {
+                name: SYMLINK_NAME2.to_string(),
+                target: "/nix/store/somewhereelse".to_string(),
+            })),
+        }),
+        ..Default::default()
+    };
+    path_info_service.put(path_info).expect("must succeed");
+}
+
+fn populate_directory_with_keep(
+    blob_service: Arc<dyn BlobService>,
+    directory_service: Arc<dyn DirectoryService>,
+    path_info_service: Arc<dyn PathInfoService>,
+) {
+    // upload empty blob
+    let mut bw = blob_service.open_write();
+    assert_eq!(
+        fixtures::EMPTY_BLOB_DIGEST.to_vec(),
+        bw.close().expect("must succeed closing").to_vec(),
+    );
+
+    // upload directory
+    directory_service
+        .put(fixtures::DIRECTORY_WITH_KEEP.clone())
+        .expect("must succeed uploading");
+
+    // upload pathinfo
+    let path_info = PathInfo {
+        node: Some(proto::Node {
+            node: Some(proto::node::Node::Directory(DirectoryNode {
+                name: DIRECTORY_WITH_KEEP_NAME.to_string(),
+                digest: fixtures::DIRECTORY_WITH_KEEP.digest().to_vec(),
+                size: fixtures::DIRECTORY_WITH_KEEP.size(),
+            })),
+        }),
+        ..Default::default()
+    };
+    path_info_service.put(path_info).expect("must succeed");
+}
+
+/// Insert [PathInfo] for DIRECTORY_WITH_KEEP, but don't provide the Directory
+/// itself.
+fn populate_pathinfo_without_directory(
+    _: Arc<dyn BlobService>,
+    _: Arc<dyn DirectoryService>,
+    path_info_service: Arc<dyn PathInfoService>,
+) {
+    // upload pathinfo
+    let path_info = PathInfo {
+        node: Some(proto::Node {
+            node: Some(proto::node::Node::Directory(DirectoryNode {
+                name: DIRECTORY_WITH_KEEP_NAME.to_string(),
+                digest: fixtures::DIRECTORY_WITH_KEEP.digest().to_vec(),
+                size: fixtures::DIRECTORY_WITH_KEEP.size(),
+            })),
+        }),
+        ..Default::default()
+    };
+    path_info_service.put(path_info).expect("must succeed");
+}
+
+/// Insert , but don't provide the blob .keep is pointing to
+fn populate_blob_a_without_blob(
+    _: Arc<dyn BlobService>,
+    _: Arc<dyn DirectoryService>,
+    path_info_service: Arc<dyn PathInfoService>,
+) {
+    // Create a PathInfo for blob A
+    let path_info = PathInfo {
+        node: Some(proto::Node {
+            node: Some(proto::node::Node::File(FileNode {
+                name: BLOB_A_NAME.to_string(),
+                digest: fixtures::BLOB_A_DIGEST.to_vec(),
+                size: fixtures::BLOB_A.len() as u32,
+                executable: false,
+            })),
+        }),
+        ..Default::default()
+    };
+    path_info_service.put(path_info).expect("must succeed");
+}
+
+fn populate_directory_complicated(
+    blob_service: Arc<dyn BlobService>,
+    directory_service: Arc<dyn DirectoryService>,
+    path_info_service: Arc<dyn PathInfoService>,
+) {
+    // upload empty blob
+    let mut bw = blob_service.open_write();
+    assert_eq!(
+        fixtures::EMPTY_BLOB_DIGEST.to_vec(),
+        bw.close().expect("must succeed closing").to_vec(),
+    );
+
+    // upload inner directory
+    directory_service
+        .put(fixtures::DIRECTORY_WITH_KEEP.clone())
+        .expect("must succeed uploading");
+
+    // uplodad parent directory
+    directory_service
+        .put(fixtures::DIRECTORY_COMPLICATED.clone())
+        .expect("must succeed uploading");
+
+    // upload pathinfo
+    let path_info = PathInfo {
+        node: Some(proto::Node {
+            node: Some(proto::node::Node::Directory(DirectoryNode {
+                name: DIRECTORY_COMPLICATED_NAME.to_string(),
+                digest: fixtures::DIRECTORY_COMPLICATED.digest().to_vec(),
+                size: fixtures::DIRECTORY_COMPLICATED.size(),
+            })),
+        }),
+        ..Default::default()
+    };
+    path_info_service.put(path_info).expect("must succeed");
+}
+
+/// Ensure mounting itself doesn't fail
+#[test]
+fn mount() {
+    // 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(tmpdir.path(), |_, _, _| {}).expect("must succeed");
+
+    fuser_session.join()
+}
+
+/// Ensure listing the root isn't allowed
+#[test]
+fn root() {
+    // 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(tmpdir.path(), |_, _, _| {}).expect("must succeed");
+
+    {
+        // read_dir succeeds, but getting the first element will fail.
+        let mut it = fs::read_dir(tmpdir).expect("must succeed");
+
+        let err = it.next().expect("must be some").expect_err("must be err");
+        assert_eq!(std::io::ErrorKind::PermissionDenied, err.kind());
+    }
+
+    fuser_session.join()
+}
+
+/// Ensure we can stat a file at the root
+#[test]
+fn stat_file_at_root() {
+    // 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(tmpdir.path(), populate_blob_a).expect("must succeed");
+
+    let p = tmpdir.path().join(BLOB_A_NAME);
+
+    // peek at the file metadata
+    let metadata = fs::metadata(p).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 read a file at the root
+#[test]
+fn read_file_at_root() {
+    // 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(tmpdir.path(), populate_blob_a).expect("must succeed");
+
+    let p = tmpdir.path().join(BLOB_A_NAME);
+
+    // read the file contents
+    let data = fs::read(p).expect("must succeed");
+
+    // ensure size and contents match
+    assert_eq!(fixtures::BLOB_A.len(), data.len());
+    assert_eq!(fixtures::BLOB_A.to_vec(), data);
+
+    fuser_session.join()
+}
+
+/// Read the target of a symlink
+#[test]
+fn symlink_readlink() {
+    // 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(tmpdir.path(), populate_symlink).expect("must succeed");
+    let p = tmpdir.path().join(SYMLINK_NAME);
+
+    let target = fs::read_link(&p).expect("must succeed");
+    assert_eq!(BLOB_A_NAME, target.to_str().unwrap());
+
+    // peek at the file metadata, which follows symlinks.
+    // this must fail, as we didn't populate the target.
+    let e = fs::metadata(&p).expect_err("must fail");
+    assert_eq!(std::io::ErrorKind::NotFound, e.kind());
+
+    // peeking at the file metadata without following symlinks will succeed.
+    let metadata = fs::symlink_metadata(&p).expect("must succeed");
+    assert!(metadata.is_symlink());
+
+    // reading from the symlink (which follows) will fail, because the target doesn't exist.
+    let e = fs::read(p).expect_err("must fail");
+    assert_eq!(std::io::ErrorKind::NotFound, e.kind());
+
+    fuser_session.join()
+}
+
+/// Read and stat a regular file through a symlink pointing to it.
+#[test]
+fn read_stat_through_symlink() {
+    // 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(tmpdir.path(), |bs: Arc<_>, ds: Arc<_>, ps: Arc<_>| {
+        populate_blob_a(bs.clone(), ds.clone(), ps.clone());
+        populate_symlink(bs, ds, ps);
+    })
+    .expect("must succeed");
+
+    let p_symlink = tmpdir.path().join(SYMLINK_NAME);
+    let p_blob = tmpdir.path().join(SYMLINK_NAME);
+
+    // peek at the file metadata, which follows symlinks.
+    // this must now return the same metadata as when statting at the target directly.
+    let metadata_symlink = fs::metadata(&p_symlink).expect("must succeed");
+    let metadata_blob = fs::metadata(&p_blob).expect("must succeed");
+    assert_eq!(metadata_blob.file_type(), metadata_symlink.file_type());
+    assert_eq!(metadata_blob.len(), metadata_symlink.len());
+
+    // reading from the symlink (which follows) will return the same data as if
+    // we were reading from the file directly.
+    assert_eq!(
+        std::fs::read(p_blob).expect("must succeed"),
+        std::fs::read(p_symlink).expect("must succeed"),
+    );
+
+    fuser_session.join()
+}
+
+/// Read a directory in the root, and validate some attributes.
+#[test]
+fn read_stat_directory() {
+    // 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(tmpdir.path(), populate_directory_with_keep).expect("must succeed");
+
+    let p = tmpdir.path().join(DIRECTORY_WITH_KEEP_NAME);
+
+    // peek at the metadata of the directory
+    let metadata = fs::metadata(&p).expect("must succeed");
+    assert!(metadata.is_dir());
+    assert!(metadata.permissions().readonly());
+
+    fuser_session.join()
+}
+
+#[test]
+/// Read a blob inside a directory. This ensures we successfully populate directory data.
+fn read_blob_inside_dir() {
+    // 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(tmpdir.path(), populate_directory_with_keep).expect("must succeed");
+
+    let p = tmpdir.path().join(DIRECTORY_WITH_KEEP_NAME).join(".keep");
+
+    // peek at metadata.
+    let metadata = fs::metadata(&p).expect("must succeed");
+    assert!(metadata.is_file());
+    assert!(metadata.permissions().readonly());
+
+    // read from it
+    let data = fs::read(&p).expect("must succeed");
+    assert_eq!(fixtures::EMPTY_BLOB_CONTENTS.to_vec(), data);
+
+    fuser_session.join()
+}
+
+#[test]
+/// Read a blob inside a directory inside a directory. This ensures we properly
+/// populate directories as we traverse down the structure.
+fn read_blob_deep_inside_dir() {
+    // 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(tmpdir.path(), populate_directory_complicated).expect("must succeed");
+
+    let p = tmpdir
+        .path()
+        .join(DIRECTORY_COMPLICATED_NAME)
+        .join("keep")
+        .join(".keep");
+
+    // peek at metadata.
+    let metadata = fs::metadata(&p).expect("must succeed");
+    assert!(metadata.is_file());
+    assert!(metadata.permissions().readonly());
+
+    // read from it
+    let data = fs::read(&p).expect("must succeed");
+    assert_eq!(fixtures::EMPTY_BLOB_CONTENTS.to_vec(), data);
+
+    fuser_session.join()
+}
+
+/// Ensure readdir works.
+#[test]
+fn readdir() {
+    // 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(tmpdir.path(), populate_directory_complicated).expect("must succeed");
+
+    let p = tmpdir.path().join(DIRECTORY_COMPLICATED_NAME);
+
+    {
+        // read_dir should succeed. Collect all elements
+        let elements: Vec<_> = fs::read_dir(p)
+            .expect("must succeed")
+            .map(|e| e.expect("must not be err"))
+            .collect();
+
+        assert_eq!(3, elements.len(), "number of elements should be 3"); // rust skips . and ..
+
+        // We explicitly look at specific positions here, because we always emit
+        // them ordered.
+
+        // ".keep", 0 byte file.
+        let e = &elements[0];
+        assert_eq!(".keep", e.file_name());
+        assert!(e.file_type().expect("must succeed").is_file());
+        assert_eq!(0, e.metadata().expect("must succeed").len());
+
+        // "aa", symlink.
+        let e = &elements[1];
+        assert_eq!("aa", e.file_name());
+        assert!(e.file_type().expect("must succeed").is_symlink());
+
+        // "keep", directory
+        let e = &elements[2];
+        assert_eq!("keep", e.file_name());
+        assert!(e.file_type().expect("must succeed").is_dir());
+    }
+
+    fuser_session.join()
+}
+
+#[test]
+/// Do a readdir deeper inside a directory, without doing readdir or stat in the parent directory.
+fn readdir_deep() {
+    // 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(tmpdir.path(), populate_directory_complicated).expect("must succeed");
+
+    let p = tmpdir.path().join(DIRECTORY_COMPLICATED_NAME).join("keep");
+
+    {
+        // read_dir should succeed. Collect all elements
+        let elements: Vec<_> = fs::read_dir(p)
+            .expect("must succeed")
+            .map(|e| e.expect("must not be err"))
+            .collect();
+
+        assert_eq!(1, elements.len(), "number of elements should be 1"); // rust skips . and ..
+
+        // ".keep", 0 byte file.
+        let e = &elements[0];
+        assert_eq!(".keep", e.file_name());
+        assert!(e.file_type().expect("must succeed").is_file());
+        assert_eq!(0, e.metadata().expect("must succeed").len());
+    }
+
+    fuser_session.join()
+}
+
+/// Check attributes match how they show up in /nix/store normally.
+#[test]
+fn check_attributes() {
+    // 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(tmpdir.path(), |bs: Arc<_>, ds: Arc<_>, ps: Arc<_>| {
+        populate_blob_a(bs.clone(), ds.clone(), ps.clone());
+        populate_directory_with_keep(bs.clone(), ds.clone(), ps.clone());
+        populate_symlink(bs, ds, ps);
+    })
+    .expect("must succeed");
+
+    let p_file = tmpdir.path().join(BLOB_A_NAME);
+    let p_directory = tmpdir.path().join(DIRECTORY_WITH_KEEP_NAME);
+    let p_symlink = tmpdir.path().join(SYMLINK_NAME);
+
+    // peek at metadata. We use symlink_metadata to ensure we don't traverse a symlink by accident.
+    let metadata_file = fs::symlink_metadata(&p_file).expect("must succeed");
+    let metadata_directory = fs::symlink_metadata(&p_directory).expect("must succeed");
+    let metadata_symlink = fs::symlink_metadata(&p_symlink).expect("must succeed");
+
+    // modes should match. We & with 0o777 to remove any higher bits.
+    assert_eq!(0o444, metadata_file.mode() & 0o777);
+    assert_eq!(0o555, metadata_directory.mode() & 0o777);
+    assert_eq!(0o444, metadata_symlink.mode() & 0o777);
+
+    // files should have the correct filesize
+    assert_eq!(fixtures::BLOB_A.len() as u64, metadata_file.len());
+    // directories should have their "size" as filesize
+    assert_eq!(
+        fixtures::DIRECTORY_WITH_KEEP.size() as u64,
+        metadata_directory.size()
+    );
+
+    for metadata in &[&metadata_file, &metadata_directory, &metadata_symlink] {
+        // uid and gid should be 0.
+        assert_eq!(0, metadata.uid());
+        assert_eq!(0, metadata.gid());
+
+        // all times should be set to the unix epoch.
+        assert_eq!(0, metadata.atime());
+        assert_eq!(0, metadata.mtime());
+        assert_eq!(0, metadata.ctime());
+        // crtime seems MacOS only
+    }
+
+    fuser_session.join()
+}
+
+#[test]
+/// Ensure we allocate the same inodes for the same directory contents.
+/// $DIRECTORY_COMPLICATED_NAME/keep contains the same data as $DIRECTORY_WITH_KEEP.
+fn compare_inodes_directories() {
+    // 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(tmpdir.path(), |bs: Arc<_>, ds: Arc<_>, ps: Arc<_>| {
+        populate_directory_with_keep(bs.clone(), ds.clone(), ps.clone());
+        populate_directory_complicated(bs, ds, ps);
+    })
+    .expect("must succeed");
+
+    let p_dir_with_keep = tmpdir.path().join(DIRECTORY_WITH_KEEP_NAME);
+    let p_sibling_dir = tmpdir.path().join(DIRECTORY_COMPLICATED_NAME).join("keep");
+
+    // peek at metadata.
+    assert_eq!(
+        fs::metadata(&p_dir_with_keep).expect("must succeed").ino(),
+        fs::metadata(&p_sibling_dir).expect("must succeed").ino()
+    );
+
+    fuser_session.join()
+}
+
+/// Ensure we allocate the same inodes for the same directory contents.
+/// $DIRECTORY_COMPLICATED_NAME/keep/,keep contains the same data as $DIRECTORY_COMPLICATED_NAME/.keep
+#[test]
+fn compare_inodes_files() {
+    // 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(tmpdir.path(), populate_directory_complicated).expect("must succeed");
+
+    let p_keep1 = tmpdir.path().join(DIRECTORY_COMPLICATED_NAME).join(".keep");
+    let p_keep2 = tmpdir
+        .path()
+        .join(DIRECTORY_COMPLICATED_NAME)
+        .join("keep")
+        .join(".keep");
+
+    // peek at metadata.
+    assert_eq!(
+        fs::metadata(&p_keep1).expect("must succeed").ino(),
+        fs::metadata(&p_keep2).expect("must succeed").ino()
+    );
+
+    fuser_session.join()
+}
+
+/// Ensure we allocate the same inode for symlinks pointing to the same targets.
+/// $DIRECTORY_COMPLICATED_NAME/aa points to the same target as SYMLINK_NAME2.
+#[test]
+fn compare_inodes_symlinks() {
+    // 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(tmpdir.path(), |bs: Arc<_>, ds: Arc<_>, ps: Arc<_>| {
+        populate_directory_complicated(bs.clone(), ds.clone(), ps.clone());
+        populate_symlink2(bs, ds, ps);
+    })
+    .expect("must succeed");
+
+    let p1 = tmpdir.path().join(DIRECTORY_COMPLICATED_NAME).join("aa");
+    let p2 = tmpdir.path().join(SYMLINK_NAME2);
+
+    // peek at metadata.
+    assert_eq!(
+        fs::symlink_metadata(&p1).expect("must succeed").ino(),
+        fs::symlink_metadata(&p2).expect("must succeed").ino()
+    );
+
+    fuser_session.join()
+}
+
+/// Check we match paths exactly.
+#[test]
+fn read_wrong_paths_in_root() {
+    // 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(tmpdir.path(), populate_blob_a).expect("must succeed");
+
+    // wrong name
+    assert!(!tmpdir
+        .path()
+        .join("00000000000000000000000000000000-tes")
+        .exists());
+
+    // invalid hash
+    assert!(!tmpdir
+        .path()
+        .join("0000000000000000000000000000000-test")
+        .exists());
+
+    // right name, must exist
+    assert!(tmpdir
+        .path()
+        .join("00000000000000000000000000000000-test")
+        .exists());
+
+    // now wrong name with right hash still may not exist
+    assert!(!tmpdir
+        .path()
+        .join("00000000000000000000000000000000-tes")
+        .exists());
+
+    fuser_session.join()
+}
+
+/// Make sure writes are not allowed
+#[test]
+fn disallow_writes() {
+    // 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(tmpdir.path(), |_, _, _| {}).expect("must succeed");
+
+    let p = tmpdir.path().join(BLOB_A_NAME);
+    let e = std::fs::File::create(&p).expect_err("must fail");
+
+    assert_eq!(std::io::ErrorKind::Unsupported, e.kind());
+
+    fuser_session.join()
+}
+
+#[test]
+/// Ensure we get an IO error if the directory service does not have the Directory object.
+fn missing_directory() {
+    if !std::path::Path::new("/dev/fuse").exists() {
+        eprintln!("skipping test");
+        return;
+    }
+    let tmpdir = TempDir::new().unwrap();
+
+    let fuser_session =
+        setup_and_mount(tmpdir.path(), populate_pathinfo_without_directory).expect("must succeed");
+
+    let p = tmpdir.path().join(DIRECTORY_WITH_KEEP_NAME);
+
+    {
+        // `stat` on the path should succeed, because it doesn't trigger the directory request.
+        fs::metadata(&p).expect("must succeed");
+
+        // However, calling either `readdir` or `stat` on a child should fail with an IO error.
+        // It fails when trying to pull the first entry, because we don't implement opendir separately
+        fs::read_dir(&p)
+            .unwrap()
+            .into_iter()
+            .next()
+            .expect("must be some")
+            .expect_err("must be err");
+
+        // rust currently sets e.kind() to Uncategorized, which isn't very
+        // helpful, so we don't look at the error more closely than that..
+        fs::metadata(p.join(".keep")).expect_err("must fail");
+    }
+
+    fuser_session.join()
+}
+
+#[test]
+/// Ensure we get an IO error if the blob service does not have the blob
+fn missing_blob() {
+    if !std::path::Path::new("/dev/fuse").exists() {
+        eprintln!("skipping test");
+        return;
+    }
+    let tmpdir = TempDir::new().unwrap();
+
+    let fuser_session =
+        setup_and_mount(tmpdir.path(), populate_blob_a_without_blob).expect("must succeed");
+
+    let p = tmpdir.path().join(BLOB_A_NAME);
+
+    {
+        // `stat` on the blob should succeed, because it doesn't trigger a request to the blob service.
+        fs::metadata(&p).expect("must succeed");
+
+        // However, calling read on the blob should fail.
+        // rust currently sets e.kind() to Uncategorized, which isn't very
+        // helpful, so we don't look at the error more closely than that..
+        fs::read(p).expect_err("must fail");
+    }
+
+    fuser_session.join()
+}