diff -r 000000000000 -r 6474c204b198 dom/system/gonk/nsVolumeMountLock.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/system/gonk/nsVolumeMountLock.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,164 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsVolumeMountLock.h"
+
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/Services.h"
+
+#include "nsIObserverService.h"
+#include "nsIPowerManagerService.h"
+#include "nsIVolume.h"
+#include "nsIVolumeService.h"
+#include "nsString.h"
+#include "nsXULAppAPI.h"
+
+#define VOLUME_MANAGER_LOG_TAG  "nsVolumeMountLock"
+#include "VolumeManagerLog.h"
+#include "nsServiceManagerUtils.h"
+#include "mozilla/dom/power/PowerManagerService.h"
+
+using namespace mozilla::dom;
+using namespace mozilla::services;
+
+namespace mozilla {
+namespace system {
+
+NS_IMPL_ISUPPORTS(nsVolumeMountLock, nsIVolumeMountLock,
+                  nsIObserver, nsISupportsWeakReference)
+
+// static
+already_AddRefed<nsVolumeMountLock>
+nsVolumeMountLock::Create(const nsAString& aVolumeName)
+{
+  DBG("nsVolumeMountLock::Create called");
+
+  nsRefPtr<nsVolumeMountLock> mountLock = new nsVolumeMountLock(aVolumeName);
+  nsresult rv = mountLock->Init();
+  NS_ENSURE_SUCCESS(rv, nullptr);
+
+  return mountLock.forget();
+}
+
+nsVolumeMountLock::nsVolumeMountLock(const nsAString& aVolumeName)
+  : mVolumeName(aVolumeName),
+    mVolumeGeneration(-1),
+    mUnlocked(false)
+{
+}
+
+//virtual
+nsVolumeMountLock::~nsVolumeMountLock()
+{
+  Unlock();
+}
+
+nsresult nsVolumeMountLock::Init()
+{
+  LOG("nsVolumeMountLock created for '%s'",
+      NS_LossyConvertUTF16toASCII(mVolumeName).get());
+
+  // Add ourselves as an Observer. It's important that we use a weak
+  // reference here. If we used a strong reference, then that reference
+  // would prevent this object from being destructed.
+  nsCOMPtr<nsIObserverService> obs = GetObserverService();
+  obs->AddObserver(this, NS_VOLUME_STATE_CHANGED, true /*weak*/);
+
+  // Request the sdcard info, so we know the state/generation without having
+  // to wait for a state change.
+  if (XRE_GetProcessType() == GeckoProcessType_Content) {
+    ContentChild::GetSingleton()->SendBroadcastVolume(mVolumeName);
+    return NS_OK;
+  }
+  nsCOMPtr<nsIVolumeService> vs = do_GetService(NS_VOLUMESERVICE_CONTRACTID);
+  NS_ENSURE_TRUE(vs, NS_ERROR_FAILURE);
+
+  vs->BroadcastVolume(mVolumeName);
+
+  return NS_OK;
+}
+
+/* void unlock (); */
+NS_IMETHODIMP nsVolumeMountLock::Unlock()
+{
+  LOG("nsVolumeMountLock released for '%s'",
+      NS_LossyConvertUTF16toASCII(mVolumeName).get());
+
+  mUnlocked = true;
+  mWakeLock = nullptr;
+
+  // While we don't really need to remove weak observers, we do so anyways
+  // since it will reduce the number of times Observe gets called.
+  nsCOMPtr<nsIObserverService> obs = GetObserverService();
+  obs->RemoveObserver(this, NS_VOLUME_STATE_CHANGED);
+  return NS_OK;
+}
+
+NS_IMETHODIMP nsVolumeMountLock::Observe(nsISupports* aSubject, const char* aTopic, const char16_t* aData)
+{
+  if (strcmp(aTopic, NS_VOLUME_STATE_CHANGED) != 0) {
+    return NS_OK;
+  }
+  if (mUnlocked) {
+    // We're not locked anymore, so we don't need to look at the notifications.
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIVolume> vol = do_QueryInterface(aSubject);
+  if (!vol) {
+    return NS_OK;
+  }
+  nsString volName;
+  vol->GetName(volName);
+  if (!volName.Equals(mVolumeName)) {
+    return NS_OK;
+  }
+  int32_t state;
+  nsresult rv = vol->GetState(&state);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (state != nsIVolume::STATE_MOUNTED) {
+    mWakeLock = nullptr;
+    mVolumeGeneration = -1;
+    return NS_OK;
+  }
+
+  int32_t   mountGeneration;
+  rv = vol->GetMountGeneration(&mountGeneration);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  DBG("nsVolumeMountLock::Observe mountGeneration = %d mVolumeGeneration = %d",
+       mountGeneration, mVolumeGeneration);
+
+  if (mVolumeGeneration == mountGeneration) {
+    return NS_OK;
+  }
+
+  // The generation changed, which means that any wakelock we may have
+  // been holding is now invalid. Grab a new wakelock for the new generation
+  // number.
+
+  mWakeLock = nullptr;
+  mVolumeGeneration = mountGeneration;
+
+  nsRefPtr<power::PowerManagerService> pmService =
+    power::PowerManagerService::GetInstance();
+  NS_ENSURE_TRUE(pmService, NS_ERROR_FAILURE);
+
+  nsString mountLockName;
+  vol->GetMountLockName(mountLockName);
+
+  ErrorResult err;
+  mWakeLock = pmService->NewWakeLock(mountLockName, nullptr, err);
+  if (err.Failed()) {
+    return err.ErrorCode();
+  }
+
+  LOG("nsVolumeMountLock acquired for '%s' gen %d",
+      NS_LossyConvertUTF16toASCII(mVolumeName).get(), mVolumeGeneration);
+  return NS_OK;
+}
+
+} // namespace system
+} // namespace mozilla