feat(runtime): stage VM runtime artifacts and writable drives in per-VM ephemeral storage by default

ts/classes.smartvm.ts

@@ -26,6 +26,8 @@ export class SmartVM {
   constructor(options: ISmartVMOptions = {}) {
     this.options = {
       dataDir: options.dataDir || '/tmp/.smartvm',
+      runtimeDir: options.runtimeDir || this.getDefaultRuntimeDir(),
+      ephemeralWritableDrives: options.ephemeralWritableDrives ?? true,
       arch: options.arch || 'x86_64',
       bridgeName: options.bridgeName || 'svbr0',
       subnet: options.subnet || '172.30.0.0/24',
@@ -57,6 +59,30 @@ export class SmartVM {
     });
   }
 
+  private getDefaultRuntimeDir(): string {
+    const tmpfsDir = '/dev/shm';
+    try {
+      if (plugins.fs.existsSync(tmpfsDir) && plugins.fs.statSync(tmpfsDir).isDirectory()) {
+        return plugins.path.join(tmpfsDir, '.smartvm', 'runtime');
+      }
+    } catch {
+      // Fall back to os.tmpdir() below.
+    }
+    return plugins.path.join(plugins.os.tmpdir(), '.smartvm', 'runtime');
+  }
+
+  public getRuntimeDir(): string {
+    return this.options.runtimeDir!;
+  }
+
+  private sanitizePathPart(value: string): string {
+    const sanitized = value.replace(/[^a-zA-Z0-9._-]/g, '_');
+    if (!sanitized || sanitized === '.' || sanitized === '..') {
+      return 'item';
+    }
+    return sanitized;
+  }
+
   /**
    * Ensure the Firecracker binary is available.
    * Downloads it if not present.
@@ -110,8 +136,9 @@ export class SmartVM {
     // Generate VM ID if not provided
     const vmId = config.id || plugins.smartunique.uuid4();
 
-    // Generate socket path
-    const socketPath = this.imageManager.getSocketPath(vmId);
+    // Keep per-VM runtime artifacts in tmpfs by default.
+    const vmRuntimeDir = plugins.path.join(this.options.runtimeDir!, this.sanitizePathPart(vmId));
+    const socketPath = plugins.path.join(vmRuntimeDir, 'firecracker.sock');
 
     // Create MicroVM instance
     const vm = new MicroVM(
@@ -120,6 +147,10 @@ export class SmartVM {
       this.firecrackerBinaryPath!,
       socketPath,
       this.networkManager,
+      {
+        runtimeDir: this.options.runtimeDir,
+        ephemeralWritableDrives: this.options.ephemeralWritableDrives,
+      },
     );
 
     // Register in active VMs