ui: Add support for creating GLImage instances from shared memory pools.

ui/gl/gl_image_shared_memory.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gl/gl_image_shared_memory.h"
 
 #include "base/logging.h"
 #include "base/memory/shared_memory.h"
 #include "base/numerics/safe_math.h"
 #include "base/process/process_handle.h"
+#include "base/sys_info.h"
 #include "base/trace_event/memory_allocator_dump.h"
 #include "base/trace_event/memory_dump_manager.h"
 #include "base/trace_event/process_memory_dump.h"
 #include "ui/gfx/buffer_format_util.h"
 
 namespace gfx {
 
 GLImageSharedMemory::GLImageSharedMemory(const Size& size,
                                          unsigned internalformat)
     : GLImageMemory(size, internalformat) {}
 
 GLImageSharedMemory::~GLImageSharedMemory() {
   DCHECK(!shared_memory_);
 }
 
 bool GLImageSharedMemory::Initialize(const base::SharedMemoryHandle& handle,
                                      GenericSharedMemoryId shared_memory_id,
-                                     BufferFormat format) {
+                                     BufferFormat format,
+                                     size_t offset) {
   size_t size_in_bytes;
   if (!BufferSizeForBufferFormatChecked(GetSize(), format, &size_in_bytes))
     return false;
 
   if (!base::SharedMemory::IsHandleValid(handle))
     return false;
 
   base::SharedMemory shared_memory(handle, true);
 
   // Duplicate the handle.
   base::SharedMemoryHandle duped_shared_memory_handle;
   if (!shared_memory.ShareToProcess(base::GetCurrentProcessHandle(),
                                     &duped_shared_memory_handle)) {
     DVLOG(0) << "Failed to duplicate shared memory handle.";
     return false;
   }
 
+  // Minimize the amount of adress space we use but make sure offset is a
+  // multiple of page size as required by MapAt().
+  size_t memory_offset = offset % base::SysInfo::VMAllocationGranularity();
+  size_t map_offset = base::SysInfo::VMAllocationGranularity() *
+                      (offset / base::SysInfo::VMAllocationGranularity());
+
+  base::CheckedNumeric<size_t> checked_size_to_map_in_bytes = size_in_bytes;
+  checked_size_to_map_in_bytes += memory_offset;
+  if (!checked_size_to_map_in_bytes.IsValid())
+    return false;
+
   scoped_ptr<base::SharedMemory> duped_shared_memory(
       new base::SharedMemory(duped_shared_memory_handle, true));
-  if (!duped_shared_memory->Map(size_in_bytes)) {
+  if (!duped_shared_memory->MapAt(static_cast<off_t>(map_offset),
+                                  checked_size_to_map_in_bytes.ValueOrDie())) {
     DVLOG(0) << "Failed to map shared memory.";
     return false;
   }
 
   if (!GLImageMemory::Initialize(
-          static_cast<unsigned char*>(duped_shared_memory->memory()), format)) {
+          static_cast<uint8_t*>(duped_shared_memory->memory()) + memory_offset,
+          format)) {
     return false;
   }
 
   DCHECK(!shared_memory_);
   shared_memory_ = duped_shared_memory.Pass();
   shared_memory_id_ = shared_memory_id;
   return true;
 }
 
 void GLImageSharedMemory::Destroy(bool have_context) {
@@ skipping 18 matching lines @@
                   base::trace_event::MemoryAllocatorDump::kUnitsBytes,
                   static_cast<uint64_t>(size_in_bytes));
 
   auto guid = GetGenericSharedMemoryGUIDForTracing(process_tracing_id,
                                                    shared_memory_id_);
   pmd->CreateSharedGlobalAllocatorDump(guid);
   pmd->AddOwnershipEdge(dump->guid(), guid);
 }
 
 }  // namespace gfx