diff -r 000000000000 -r 6474c204b198 memory/mozalloc/VolatileBufferAshmem.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/memory/mozalloc/VolatileBufferAshmem.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,137 @@
+/* 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 "VolatileBuffer.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/NullPtr.h"
+#include "mozilla/mozalloc.h"
+
+#include <fcntl.h>
+#include <linux/ashmem.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#ifdef MOZ_MEMORY
+#ifdef MOZ_WIDGET_ANDROID
+extern "C" int __wrap_posix_memalign(void** memptr, size_t alignment, size_t size);
+#else
+extern "C" int posix_memalign(void** memptr, size_t alignment, size_t size);
+#endif
+#endif
+
+#define MIN_VOLATILE_ALLOC_SIZE 8192
+
+namespace mozilla {
+
+VolatileBuffer::VolatileBuffer()
+  : mBuf(nullptr)
+  , mSize(0)
+  , mLockCount(0)
+  , mFd(-1)
+{
+}
+
+bool
+VolatileBuffer::Init(size_t aSize, size_t aAlignment)
+{
+  MOZ_ASSERT(!mSize && !mBuf, "Init called twice");
+  MOZ_ASSERT(!(aAlignment % sizeof(void *)),
+         "Alignment must be multiple of pointer size");
+
+  mSize = aSize;
+  if (aSize < MIN_VOLATILE_ALLOC_SIZE) {
+    goto heap_alloc;
+  }
+
+  mFd = open("/" ASHMEM_NAME_DEF, O_RDWR);
+  if (mFd < 0) {
+    goto heap_alloc;
+  }
+
+  if (ioctl(mFd, ASHMEM_SET_SIZE, mSize) < 0) {
+    close(mFd);
+    mFd = -1;
+    goto heap_alloc;
+  }
+
+  mBuf = mmap(nullptr, mSize, PROT_READ | PROT_WRITE, MAP_SHARED, mFd, 0);
+  if (mBuf != MAP_FAILED) {
+    return true;
+  }
+
+heap_alloc:
+#ifdef MOZ_MEMORY
+#ifdef MOZ_WIDGET_ANDROID
+  __wrap_posix_memalign(&mBuf, aAlignment, aSize);
+#else
+  posix_memalign(&mBuf, aAlignment, aSize);
+#endif
+#else
+  mBuf = memalign(aAlignment, aSize);
+#endif
+  return !!mBuf;
+}
+
+VolatileBuffer::~VolatileBuffer()
+{
+  if (OnHeap()) {
+    free(mBuf);
+  } else {
+    munmap(mBuf, mSize);
+    close(mFd);
+  }
+}
+
+bool
+VolatileBuffer::Lock(void** aBuf)
+{
+  MOZ_ASSERT(mBuf, "Attempting to lock an uninitialized VolatileBuffer");
+
+  *aBuf = mBuf;
+  if (++mLockCount > 1 || OnHeap()) {
+    return true;
+  }
+
+  // Zero offset and zero length means we want to pin/unpin the entire thing.
+  struct ashmem_pin pin = { 0, 0 };
+  return ioctl(mFd, ASHMEM_PIN, &pin) == ASHMEM_NOT_PURGED;
+}
+
+void
+VolatileBuffer::Unlock()
+{
+  MOZ_ASSERT(mLockCount > 0, "VolatileBuffer unlocked too many times!");
+  if (--mLockCount || OnHeap()) {
+    return;
+  }
+
+  struct ashmem_pin pin = { 0, 0 };
+  ioctl(mFd, ASHMEM_UNPIN, &pin);
+}
+
+bool
+VolatileBuffer::OnHeap() const
+{
+  return mFd < 0;
+}
+
+size_t
+VolatileBuffer::HeapSizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
+{
+  return OnHeap() ? aMallocSizeOf(mBuf) : 0;
+}
+
+size_t
+VolatileBuffer::NonHeapSizeOfExcludingThis() const
+{
+  if (OnHeap()) {
+    return 0;
+  }
+
+  return (mSize + (PAGE_SIZE - 1)) & PAGE_MASK;
+}
+
+} // namespace mozilla