openwrt's vmm waits for cvdalloc.

openwrt uses a vmm to run a Wi-Fi access point, using a 802.11
hardware simulator connected to a tap device. Without cvdalloc, it
assumes this device was already created by cuttlefish-host-resources.
With cvdalloc, openwrt's vmm will need to wait for cvdalloc to complete
in order to use the tap device it creates.

The obvious way to do this is to use WaitForAvailability on cvdalloc's
launcher. However, cvdalloc's launcher is already a VmmDependencyCommand
for the instance's vmm, and if both openwrt's and cvdalloc's launcher are
executing at the same time, we have two contending reads on cvdalloc's
socketpair, which complicates matters.

We could Wait and Post twice on the socket for notification, but that is
rather ugly since that means we couple the number of socket Wait'ers to
the cvdalloc binary unnecessarily. Instead, we guard WaitForAvailability
by a mutex, so that there is always only one Wait'er at a time, and make
WaitForAvailability idempotent, so that the second Wait need not
actually attempt to read on the underlying socket.

Author: 3405691582

base/cvd/cuttlefish/host/commands/run_cvd/launch/BUILD.bazel

@@ -288,6 +288,7 @@ cf_cc_library(
     deps = [
         "//cuttlefish/common/libs/utils:json",
         "//cuttlefish/common/libs/utils:result",
+        "//cuttlefish/host/commands/run_cvd/launch:cvdalloc",
         "//cuttlefish/host/commands/run_cvd/launch:log_tee_creator",
         "//cuttlefish/host/commands/run_cvd/launch:wmediumd_server",
         "//cuttlefish/host/libs/command_util",

base/cvd/cuttlefish/host/commands/run_cvd/launch/cvdalloc.cpp

@@ -21,6 +21,7 @@
 #include <sys/stat.h>
 
 #include <chrono>
+#include <mutex>
 #include <string>
 #include <string_view>
 #include <unordered_set>
@@ -47,7 +48,7 @@ constexpr std::chrono::seconds kCvdAllocateTimeout = std::chrono::seconds(30);
 constexpr std::chrono::seconds kCvdTeardownTimeout = std::chrono::seconds(2);
 
 Cvdalloc::Cvdalloc(const CuttlefishConfig::InstanceSpecific& instance)
-    : instance_(instance) {}
+    : instance_(instance), status_(CvdallocStatus::kUnknown) {}
 
 Result<std::vector<MonitorCommand>> Cvdalloc::Commands() {
   std::string path = CvdallocBinary();
@@ -67,10 +68,17 @@ bool Cvdalloc::Enabled() const { return instance_.use_cvdalloc(); }
 std::unordered_set<SetupFeature *> Cvdalloc::Dependencies() const { return {}; }
 
 Result<void> Cvdalloc::WaitForAvailability() {
-  LOG(INFO) << "cvdalloc (run_cvd): waiting to finish allocation.";
-  CF_EXPECT(cvdalloc::Wait(socket_, kCvdAllocateTimeout),
-            "cvdalloc (run_cvd): Wait failed");
-  LOG(INFO) << "cvdalloc (run_cvd): allocation is done.";
+  std::lock_guard<std::mutex> lock(availability_mutex_);
+  CF_EXPECT(status_ != CvdallocStatus::kFailed);
+  if (status_ == CvdallocStatus::kUnknown) {
+    LOG(INFO) << "cvdalloc (run_cvd): waiting to finish allocation.";
+    status_ = CvdallocStatus::kFailed;
+    CF_EXPECT(cvdalloc::Wait(socket_, kCvdAllocateTimeout),
+              "cvdalloc (run_cvd): Wait failed");
+    LOG(INFO) << "cvdalloc (run_cvd): allocation is done.";
+    status_ = CvdallocStatus::kAvailable;
+  }
+  LOG(INFO) << "cvdalloc (run_cvd): available.";
 
   return {};
 }

base/cvd/cuttlefish/host/commands/run_cvd/launch/cvdalloc.h

@@ -29,6 +29,12 @@
 
 namespace cuttlefish {
 
+enum class CvdallocStatus {
+  kUnknown = 0,
+  kAvailable,
+  kFailed
+};
+
 class Cvdalloc : public vm_manager::VmmDependencyCommand {
  public:
   INJECT(Cvdalloc(const CuttlefishConfig::InstanceSpecific &instance));
@@ -49,6 +55,8 @@ class Cvdalloc : public vm_manager::VmmDependencyCommand {
 
   const CuttlefishConfig::InstanceSpecific &instance_;
   SharedFD socket_, their_socket_;
+  std::mutex availability_mutex_;
+  CvdallocStatus status_;
 };
 
 fruit::Component<fruit::Required<const CuttlefishConfig::InstanceSpecific>>

base/cvd/cuttlefish/host/commands/run_cvd/launch/open_wrt.cpp

@@ -27,6 +27,7 @@
 
 #include "cuttlefish/common/libs/utils/json.h"
 #include "cuttlefish/common/libs/utils/result.h"
+#include "cuttlefish/host/commands/run_cvd/launch/cvdalloc.h"
 #include "cuttlefish/host/commands/run_cvd/launch/log_tee_creator.h"
 #include "cuttlefish/host/commands/run_cvd/launch/wmediumd_server.h"
 #include "cuttlefish/host/libs/command_util/snapshot_utils.h"
@@ -48,12 +49,14 @@ class OpenWrt : public CommandSource {
   INJECT(OpenWrt(const CuttlefishConfig& config,
                  const CuttlefishConfig::EnvironmentSpecific& environment,
                  const CuttlefishConfig::InstanceSpecific& instance,
-                 LogTeeCreator& log_tee, WmediumdServer& wmediumd_server))
+                 LogTeeCreator& log_tee, WmediumdServer& wmediumd_server,
+                 Cvdalloc& cvdalloc))
       : config_(config),
         environment_(environment),
         instance_(instance),
         log_tee_(log_tee),
-        wmediumd_server_(wmediumd_server) {}
+        wmediumd_server_(wmediumd_server),
+        cvdalloc_(cvdalloc) {}
 
   // CommandSource
   Result<std::vector<MonitorCommand>> Commands() override {
@@ -62,7 +65,11 @@ class OpenWrt : public CommandSource {
     CrosvmBuilder ap_cmd;
 
     ap_cmd.Cmd().AddPrerequisite([this]() -> Result<void> {
-      return wmediumd_server_.WaitForAvailability();
+      if (cvdalloc_.Enabled()) {
+        CF_EXPECT(cvdalloc_.WaitForAvailability());
+      }
+      CF_EXPECT(wmediumd_server_.WaitForAvailability());
+      return {};
     });
 
     std::string first_time_argument;
@@ -183,15 +190,17 @@ class OpenWrt : public CommandSource {
   const CuttlefishConfig::InstanceSpecific& instance_;
   LogTeeCreator& log_tee_;
   WmediumdServer& wmediumd_server_;
+  Cvdalloc& cvdalloc_;
 
   static constexpr int kOpenwrtVmResetExitCode = 32;
 };
 
 }  // namespace
 
-fruit::Component<fruit::Required<
-    const CuttlefishConfig, const CuttlefishConfig::EnvironmentSpecific,
-    const CuttlefishConfig::InstanceSpecific, LogTeeCreator, WmediumdServer>>
+fruit::Component<fruit::Required<const CuttlefishConfig,
+                                 const CuttlefishConfig::EnvironmentSpecific,
+                                 const CuttlefishConfig::InstanceSpecific,
+                                 LogTeeCreator, WmediumdServer, Cvdalloc>>
 OpenWrtComponent() {
   return fruit::createComponent()
       .addMultibinding<CommandSource, OpenWrt>()

base/cvd/cuttlefish/host/commands/run_cvd/launch/open_wrt.h

@@ -17,15 +17,17 @@
 
 #include <fruit/fruit.h>
 
+#include "cuttlefish/host/commands/run_cvd/launch/cvdalloc.h"
 #include "cuttlefish/host/commands/run_cvd/launch/log_tee_creator.h"
 #include "cuttlefish/host/commands/run_cvd/launch/wmediumd_server.h"
 #include "cuttlefish/host/libs/config/cuttlefish_config.h"
 
 namespace cuttlefish {
 
-fruit::Component<fruit::Required<
-    const CuttlefishConfig, const CuttlefishConfig::EnvironmentSpecific,
-    const CuttlefishConfig::InstanceSpecific, LogTeeCreator, WmediumdServer>>
+fruit::Component<fruit::Required<const CuttlefishConfig,
+                                 const CuttlefishConfig::EnvironmentSpecific,
+                                 const CuttlefishConfig::InstanceSpecific,
+                                 LogTeeCreator, WmediumdServer, Cvdalloc>>
 OpenWrtComponent();
 
 }  // namespace cuttlefish