sausage-vfs: review fixes (fallible growth, symlink flags, stream cancel, sized reads, timestamps, error kinds, linker shadowing)

API: Layer::stat(path, follow), Layer::readlink, Open::follow,
Stat::symlink and Entry::symlink. Process::idle documents the shutdown
order: abort, await the task, await idle, release locks.

vfs/tests/wasi.rs

@@ -55,6 +55,14 @@ async fn run(topic: &str, shared: Arc<Memory>) {
     let (engine, component) = guest();
     let world = tempfile::tempdir().unwrap();
     std::fs::create_dir(world.path().join("tmp")).unwrap();
+    let outside = tempfile::tempdir().unwrap();
+    if topic == "review_links" {
+        std::fs::create_dir(world.path().join("target")).unwrap();
+        std::fs::write(world.path().join("target/keep"), b"keep").unwrap();
+        std::fs::write(outside.path().join("secret"), b"secret").unwrap();
+        std::os::unix::fs::symlink("target", world.path().join("link")).unwrap();
+        std::os::unix::fs::symlink(outside.path(), world.path().join("outside-link")).unwrap();
+    }
     let mut mounts = Mounts::default();
     mounts.mount(
         "/",
@@ -73,13 +81,20 @@ async fn run(topic: &str, shared: Arc<Memory>) {
         table: &mut s.table,
     })
     .unwrap();
+    let mut wasi = WasiCtxBuilder::new();
+    wasi.inherit_stdio().env("VFS_TOPIC", topic);
+    if topic == "review_preopen" {
+        wasi.preopened_dir(
+            world.path(),
+            "/native",
+            wasmtime_wasi::filesystem::FsPerms::ReadWrite,
+        )
+        .unwrap();
+    }
     let mut store = Store::new(
         engine,
         State {
-            wasi: WasiCtxBuilder::new()
-                .inherit_stdio()
-                .env("VFS_TOPIC", topic)
-                .build(),
+            wasi: wasi.build(),
             table: ResourceTable::new(),
             fs: Adapter::new(mounts),
         },
@@ -150,3 +165,47 @@ async fn sqlite_transactions() {
 async fn named_temporary_files() {
     isolated("tempfile").await;
 }
+
+/// Stream drop preserves writes and small reads observe later mutations.
+#[tokio::test(flavor = "multi_thread")]
+async fn review_streams() {
+    isolated("review_streams").await;
+}
+
+/// Timestamp conversion reports overflow and accepts directories.
+#[tokio::test(flavor = "multi_thread")]
+async fn review_times() {
+    isolated("review_times").await;
+}
+
+/// Path errors distinguish trailing slashes, busy roots, and ordinary files.
+#[tokio::test(flavor = "multi_thread")]
+async fn review_paths() {
+    isolated("review_paths").await;
+}
+
+/// Symlink traversal does not delete targets or escape the host root.
+#[tokio::test(flavor = "multi_thread")]
+async fn review_links() {
+    isolated("review_links").await;
+}
+
+/// The guest sees only the virtual root preopen.
+#[tokio::test(flavor = "multi_thread")]
+async fn review_preopen() {
+    isolated("review_preopen").await;
+}
+
+/// Adding the adapter restores duplicate-import errors on the caller's linker.
+#[test]
+fn linker_shadowing_is_reset() {
+    let engine = Engine::default();
+    let mut linker = Linker::<State>::new(&engine);
+    wasmtime_wasi::p2::add_to_linker_async(&mut linker).unwrap();
+    adapter::add_to_linker(&mut linker, |s| View {
+        adapter: &mut s.fs,
+        table: &mut s.table,
+    })
+    .unwrap();
+    assert!(wasmtime_wasi::p2::add_to_linker_async(&mut linker).is_err());
+}