Actor-served files: /actor/<id>/fs/

File operations under /actor/<id>/fs/ become messages from `fs` to <id>
(fs_read, fs_write, fs_mkdir, fs_remove, fs_rename) with a 10 s timeout.
vfs.rs wraps the wasi:filesystem implementation of wasmtime-wasi.

cli/src/runtime.rs

@@ -4,7 +4,7 @@
 //! NDJSON lines to its stdin and reads NDJSON lines from its stdout.
 
 use std::path::{Path, PathBuf};
-use std::sync::Arc;
+use std::sync::{Arc, Weak};
 use std::time::Duration;
 
 use anyhow::{Context, Result};
@@ -14,10 +14,15 @@ use tokio::task::JoinHandle;
 use wasmtime::component::{Component, Linker, ResourceTable};
 use wasmtime::{Config, Engine, Store};
 use wasmtime_wasi::cli::{AsyncStdinStream, AsyncStdoutStream};
+use wasmtime_wasi::filesystem::WasiFilesystemCtxView;
 use wasmtime_wasi::p2::bindings::Command;
+use wasmtime_wasi::p2::bindings::filesystem;
 use wasmtime_wasi::{FsPerms, I32Exit, WasiCtx, WasiCtxView, WasiView};
 use wasmtime_wasi_http::{WasiHttpCtx, WasiHttpCtxView, WasiHttpHooks, WasiHttpView};
 
+use crate::broker::Broker;
+use crate::vfs::{Vfs, VfsState, VfsView};
+
 /// A host folder that the guest sees at `guest`.
 #[derive(Clone, Debug)]
 pub struct Mount {
@@ -65,6 +70,11 @@ pub struct ActorState {
     table: ResourceTable,
     http: WasiHttpCtx,
     hooks: HttpHooks,
+    vfs: VfsState,
+}
+
+fn vfs_view(s: &mut ActorState) -> VfsView<'_> {
+    VfsView { inner: WasiFilesystemCtxView { ctx: s.ctx.filesystem(), table: &mut s.table }, state: &mut s.vfs }
 }
 
 impl WasiView for ActorState {
@@ -111,6 +121,10 @@ pub struct InstanceConfig {
     pub network: bool,
     pub stderr_log: PathBuf,
     pub env: Vec<(String, String)>,
+    /// The actor that runs in the instance.
+    pub actor: String,
+    /// Asks the actors that serve `/actor/<id>/fs/` (see `vfs.rs`).
+    pub broker: Weak<Broker>,
 }
 
 /// A running guest. Dropping it kills the guest.
@@ -224,6 +238,11 @@ impl Runtime {
         let mut linker: Linker<ActorState> = Linker::new(&engine);
         wasmtime_wasi::p2::add_to_linker_async(&mut linker)?;
         wasmtime_wasi_http::p2::add_only_http_to_linker_async(&mut linker)?;
+        // Replace `wasi:filesystem` with the wrapper that serves `/actor/<id>/fs/`.
+        linker.allow_shadowing(true);
+        filesystem::types::add_to_linker::<ActorState, Vfs>(&mut linker, vfs_view)?;
+        filesystem::preopens::add_to_linker::<ActorState, Vfs>(&mut linker, vfs_view)?;
+        linker.allow_shadowing(false);
 
         // Time slices: every 10 ms each running guest yields to the scheduler.
         let ticker = engine.clone();
@@ -274,6 +293,7 @@ impl Runtime {
             table: ResourceTable::new(),
             http: WasiHttpCtx::new(),
             hooks: HttpHooks { allow: cfg.network },
+            vfs: VfsState::new(cfg.broker.clone(), cfg.actor.clone()),
         };
 
         let (line_tx, line_rx) = mpsc::channel(1024);