Pass file Regions along with FDs to child processes on Android

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 "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/sys_info.h"
 
 namespace base {
 
 const MemoryMappedFile::Region MemoryMappedFile::Region::kWholeFile(
     base::LINKER_INITIALIZED);
 
 MemoryMappedFile::Region::Region(base::LinkerInitialized) : offset(0), size(0) {
 }
 
+MemoryMappedFile::Region::Region() : offset(0), size(0) {

[Lei Zhang, 2015/05/28 18:55:53]

Perhaps this one should be (-1, -1) to indicate invalidness.

[agrieve, 2015/05/28 19:13:24]

sgtm (done)

+}
+
 MemoryMappedFile::Region::Region(int64 offset, int64 size)
     : offset(offset), size(size) {
-  DCHECK_GE(offset, 0);

[Lei Zhang, 2015/05/28 18:55:53]

why remove the DCHECKs?

[agrieve, 2015/05/28 19:13:24]

There are times (like when going through jni) where it's nice to be able to
convert to two int64s and back again. These DCHECKs prevent doing so for
kWholeFile.

[Lei Zhang, 2015/05/29 21:14:09]

Assuming we stick with -1 to indicate invalidness, and you would only want to
reconstruct valid Regions from JNI, how about:

if (size == 0) {
  DCHECK_EQ(0, offset);
} else {
  DCHECK_GE(offset, 0);
  DCHECK_GT(size, 0);
}

[agrieve, 2015/06/01 14:50:05]

This wouldn't allow you to convert an invalid region (-1,-1) to size/offset and
back to a region (as is done in JNI).

How about I move this check to Initialize (which I've gone ahead and done)? This
way we still have the same check where it counts, and Region gets to behave more
like a POD.

-  DCHECK_GT(size, 0);
 }
 
 bool MemoryMappedFile::Region::operator==(
     const MemoryMappedFile::Region& other) const {
   return other.offset == offset && other.size == size;
 }
 
 MemoryMappedFile::~MemoryMappedFile() {
   CloseHandles();
 }
@@ skipping 49 matching lines @@
   // Sadly, on Windows, the mmap alignment is not just equal to the page size.
   const int64 mask = static_cast<int64>(SysInfo::VMAllocationGranularity()) - 1;
   DCHECK_LT(mask, std::numeric_limits<int32>::max());
   *offset = start & mask;
   *aligned_start = start & ~mask;
   *aligned_size = (size + *offset + mask) & ~mask;
 }
 #endif
 
 }  // namespace base