bunpen: barebones pasta integration

totally untested, except that it builds

pkgs/additional/bunpen/restrict/ns/namespace.ha

@@ -107,7 +107,7 @@ export fn namespace_restrict(what: *restrict::resources) void = {
     case restrict::net_none =>
       errors::ext::check("namespace: unshare net", rt::ext::unshare(rt::ext::clone_flag::NEWNET));
     case let subset: restrict::net_subset =>
-      errors::ext::check("namespace: unshare net", rt::ext::unshare(rt::ext::clone_flag::NEWNET));
+      setup_pasta(subset);
     case restrict::net_all =>
       log::println("[namespace] keeping net namespace");
   };
@@ -164,19 +164,22 @@ type ns_ctx = struct {
 // - in the parent: wait for the child, then propagate its exit status
 fn fork_and_propagate() (void | os::exec::error) = {
   match (os::exec::fork()?) {
-    case let child_pid: os::exec::process =>
-      forward_signals(child_pid);
-      log::println("[namespace/fork] signals configured");
-      let status = wait_child(child_pid)?;
-      let rc = rt::wexitstatus(status.status);
-      // TODO: if the child exited due to a signal (e.g. SIGTERM), we (confusingly?) exit 0.
-      // seems correct behavior may be to send the same termination signal to ourselves.
-      log::printfln("[namespace/fork] child exited with {}; forwarding as {}", status.status, rc);
-      os::exit(rc);  // propagate exit code
+    case let child_pid: os::exec::process => return wait_and_propagate(child_pid);
     case => log::println("[namespace/fork] continuing as child");
   };
 };
 
+fn wait_and_propagate(child_pid: os::exec::process) (void | os::exec::error) = {
+  forward_signals(child_pid);
+  log::println("[namespace/fork] signals configured");
+  let status = wait_child(child_pid)?;
+  let rc = rt::wexitstatus(status.status);
+  // TODO: if the child exited due to a signal (e.g. SIGTERM), we (confusingly?) exit 0.
+  // seems correct behavior may be to send the same termination signal to ourselves.
+  log::printfln("[namespace/fork] child exited with {}; forwarding as {}", status.status, rc);
+  os::exit(rc);  // propagate exit code
+};
+
 fn wait_child(child_pid: os::exec::process) (os::exec::status | os::exec::error) = {
   for (true) {
     match (os::exec::wait(&child_pid)) {

pkgs/additional/bunpen/restrict/ns/pasta.ha

@@ -0,0 +1,46 @@
+// vim: set shiftwidth=2 :
+use errors;
+use errors::ext;
+use fmt;
+use os;
+use os::exec;
+use restrict;
+use rt;
+use rt::ext;
+
+fn setup_pasta(net: restrict::net_subset) void = {
+  // `pasta PID [options]`: creates a device in the netns of PID.
+  // ordering:
+  // 1. fork
+  // 2. child: enter netns, signal parent.
+  // 3. parent: fork and spawn `pasta --pid /proc/fd/$N`
+  //    then dumbly wait on child until completion
+  // 4. child: wait for `pasta` to signal readiness on fd `$N`
+  //
+  // after that, we can continue on & exec into the user code
+  //
+  // TODO: this currently lacks the synchronization described above
+
+  match (os::exec::fork()) {
+    case let child_pid: os::exec::process =>
+      errors::ext::check("setup_pasta: attach", attach_pasta(child_pid));
+      errors::ext::check("setup_pasta: wait", wait_and_propagate(child_pid));
+    case void =>
+      errors::ext::check("namespace: unshare net", rt::ext::unshare(rt::ext::clone_flag::NEWNET));
+    case let e: os::exec::error =>
+      errors::ext::check("setup_pasta: fork", e);
+  };
+};
+
+// spawn pasta as a separate process, and have it attach to the netns of the given pid.
+fn attach_pasta(child: os::exec::process) (void | os::exec::error | rt::errno) = {
+  return match (os::exec::fork()?) {
+    case let pasta_pid: os::exec::process => yield void;
+    case void =>
+      let pidstr = fmt::asprint(child: int);
+      defer free(pidstr);
+      let pasta_args = [ "pasta", pidstr ];
+      // TODO: append dns, gateway arguments to `pasta`.
+      yield rt::ext::execvpe("pasta", pasta_args, os::getenvs());
+  };
+};