service: Add a README.md to nydus-service

README.md

@@ -137,6 +137,11 @@ The containerd remote snapshotter plugin [nydus-snapshotter](https://github.com/
 
 In the future, `zstd::chunked` can work in this way as well.
 
+## Reuse Nydus Services
+
+Using the key features of nydus as native in your project without preparing and invoking `nydusd` deliberately, [nydus-service](./service/README.md) helps to reuse the core services of nyuds.
+
+
 ## Documentation
 
 Browse the documentation to learn more. Here are some topics you may be interested in:

service/README.md

@@ -0,0 +1,157 @@
+# nydus-service
+
+The `nydus-service` crate helps to reuse the core services of nydus, allowing you to integrate nydus services into your project elegantly and easily. It provides:
+
+* fuse service
+* virtio-fs service
+* fscache service
+* blobcache service
+
+It also supplies the nydus daemon and the daemon controller to help manage these services.
+
+## Why you need
+
+You're supposed to know that `nydusd` running as daemon to expose a [FUSE](https://www.kernel.org/doc/html/latest/filesystems/fuse.html) mountpoint, a [Virtio-FS](https://virtio-fs.gitlab.io/) mountpoint or an [EROFS](https://docs.kernel.org/filesystems/erofs.html) mountpoint inside guest for containers to access, and it provides key features include:
+
+- Container images are downloaded on demand
+- Chunk level data deduplication
+- Flatten image metadata and data to remove all intermediate layers
+- Only usable image data is saved when building a container image
+- Only usable image data is downloaded when running a container
+- End-to-end image data integrity
+- Compatible with the OCI artifacts spec and distribution spec
+- Integrated with existing CNCF project Dragonfly to support image distribution in large clusters
+- Different container image storage backends are supported
+
+If you want to use these features as native in your project without preparing and invoking `nydusd` deliberately, `nydus-service` is just born for this.
+
+## How to use
+
+For example, reuse the fuse service with `nydus-service` in three steps.
+
+**prepare the config**:
+
+```rust
+{
+  "device": {
+    "backend": {
+      "type": "registry",
+      "config": {
+        "scheme": "",
+        "skip_verify": true,
+        "timeout": 5,
+        "connect_timeout": 5,
+        "retry_limit": 4,
+        "auth": "YOUR_LOGIN_AUTH="
+      }
+    },
+    "cache": {
+      "type": "blobcache",
+      "config": {
+        "work_dir": "cache"
+      }
+    }
+  },
+  "mode": "direct",
+  "digest_validate": false,
+  "iostats_files": false,
+  "enable_xattr": true,
+  "fs_prefetch": {
+    "enable": true,
+    "threads_count": 4
+  }
+}
+```
+
+**create a daemon**:
+
+```Rust
+static ref DAEMON_CONTROLLER: DaemonController = DaemonController::default()
+
+let cmd = FsBackendMountCmd {
+    fs_type: FsBackendType::Rafs,
+    // Bootstrap path
+    source: bootstrap,
+    // Backend config
+    config,
+    // Virutal mountpoint
+    mountpoint: "/".to_string(),
+    // Prefetch files
+    prefetch_files: None,
+};
+
+let daemon = {
+    create_fuse_daemon(
+        // Mountpoint for the FUSE filesystem, target for `mount.fuse`
+        mountpoint,
+        // Vfs associated with the filesystem service object
+        vfs,
+        // Supervisor
+        None,
+      	// Service instance identifier
+        id,
+        // Number of working threads to serve fuse requests
+        fuse_threads,
+      	// daemon controller's waker
+        waker,
+      	// Path to the Nydus daemon administration API socket
+        Some("api_sock"),
+      	// Start Nydus daemon in upgrade mode
+        upgrade,
+      	// Mounts FUSE filesystem in rw mode
+        !writable,
+        // FUSE server failover policy
+        failvoer-policy,
+        // Request structure to mount a backend filesystem instance
+        Some(cmd),
+        BTI.to_owned(),
+    )
+    .map(|d| {
+    		info!("Fuse daemon started!");
+    		d
+    })
+    .map_err(|e| {
+       	error!("Failed in starting daemon: {}", e);
+       	e
+    })?
+};
+
+DAEMON_CONTROLLER.set_daemon(daemon);
+```
+
+**start daemon controller**:
+
+```rust
+thread::spawn(move || {
+ 	 let daemon = DAEMON_CONTROLLER.get_daemon();
+ 	 if let Some(fs) = daemon.get_default_fs_service() {
+ 	   	DAEMON_CONTROLLER.set_fs_service(fs);
+ 	 }
+
+ 	 // Run the main event loop
+ 	 if DAEMON_CONTROLLER.is_active() {
+ 	   	DAEMON_CONTROLLER.run_loop();
+	 }
+
+ 	 // Gracefully shutdown system.
+ 	 info!("nydusd quits");
+ 	 DAEMON_CONTROLLER.shutdown();
+});
+```
+
+Then, you can make the most of nydus services in your project.
+
+## Support
+
+**Platforms**:
+
+- x86_64
+- aarch64
+
+**Operating Systems**:
+
+- Linux
+
+## License
+
+This code is licensed under [Apache-2.0](LICENSE-APACHE) or [BSD-3-Clause](LICENSE-BSD-3-Clause).