Support read/write memory-mapped files.

base/files/memory_mapped_file.cc

 // Copyright 2013 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 "base/files/memory_mapped_file.h"
 
 #include <utility>
 
 #include "base/files/file_path.h"
 #include "base/logging.h"
@@ skipping 12 matching lines @@
 bool MemoryMappedFile::Region::operator!=(
     const MemoryMappedFile::Region& other) const {
   return other.offset != offset || other.size != size;
 }
 
 MemoryMappedFile::~MemoryMappedFile() {
   CloseHandles();
 }
 
 #if !defined(OS_NACL)
-bool MemoryMappedFile::Initialize(const FilePath& file_name) {
+bool MemoryMappedFile::Initialize(const FilePath& file_name, Access access) {
   if (IsValid())
     return false;
 
-  file_.Initialize(file_name, File::FLAG_OPEN | File::FLAG_READ);
+  uint32_t flags = 0;
+  switch (access) {
+    case READ_ONLY:
+      flags = File::FLAG_OPEN | File::FLAG_READ;
+      break;
+    case READ_WRITE:
+      flags = File::FLAG_OPEN | File::FLAG_READ | File::FLAG_WRITE;
+      break;
+    case READ_WRITE_EXTEND:
+      // Can't open with "extend" because no maximum size is known.
+      NOTREACHED();
+  }
+  file_.Initialize(file_name, flags);
 
   if (!file_.IsValid()) {
     DLOG(ERROR) << "Couldn't open " << file_name.AsUTF8Unsafe();
     return false;
   }
 
-  if (!MapFileRegionToMemory(Region::kWholeFile)) {
+  if (!MapFileRegionToMemory(Region::kWholeFile, access)) {
     CloseHandles();
     return false;
   }
 
   return true;
 }
 
-bool MemoryMappedFile::Initialize(File file) {
-  return Initialize(std::move(file), Region::kWholeFile);
+bool MemoryMappedFile::Initialize(File file, Access access) {
+  DCHECK_NE(READ_WRITE_EXTEND, access);
+  return Initialize(std::move(file), Region::kWholeFile, access);
 }
 
-bool MemoryMappedFile::Initialize(File file, const Region& region) {
+bool MemoryMappedFile::Initialize(File file,
+                                  const Region& region,
+                                  Access access) {
+  switch (access) {
+    case READ_WRITE_EXTEND:
+      // Ensure that the extended size is within limits of File.
+      if (region.size > std::numeric_limits<int64_t>::max() - region.offset) {
+        DLOG(ERROR) << "Region bounds exceed maximum for base::File.";
+        return false;
+      }
+      // Fall through.
+    case READ_ONLY:
+    case READ_WRITE:
+      // Ensure that the region values are valid.
+      if (region.offset < 0 || region.size < 0) {
+        DLOG(ERROR) << "Region bounds are not valid.";
+        return false;
+      }
+      break;
+  }
+
   if (IsValid())
     return false;
 
   if (region != Region::kWholeFile) {
     DCHECK_GE(region.offset, 0);
     DCHECK_GT(region.size, 0);
   }
 
   file_ = std::move(file);
 
-  if (!MapFileRegionToMemory(region)) {
+  if (!MapFileRegionToMemory(region, access)) {
     CloseHandles();
     return false;
   }
 
   return true;
 }
 
 bool MemoryMappedFile::IsValid() const {
   return data_ != NULL;
 }
 
 // static
 void MemoryMappedFile::CalculateVMAlignedBoundaries(int64_t start,
                                                     int64_t size,
                                                     int64_t* aligned_start,
                                                     int64_t* aligned_size,
                                                     int32_t* offset) {
   // Sadly, on Windows, the mmap alignment is not just equal to the page size.
   const int64_t mask =
       static_cast<int64_t>(SysInfo::VMAllocationGranularity()) - 1;
   DCHECK_LT(mask, std::numeric_limits<int32_t>::max());
   *offset = start & mask;
   *aligned_start = start & ~mask;
   *aligned_size = (size + *offset + mask) & ~mask;
 }
 #endif
 
 }  // namespace base