Disk cache: Pre-read file headers when opening files (posix).

net/disk_cache/mapped_file_win.cc

 // Copyright (c) 2011 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 "net/disk_cache/mapped_file.h"
 
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
 #include "net/disk_cache/disk_cache.h"
@@ skipping 10 matching lines @@
   section_ = CreateFileMapping(platform_file(), NULL, PAGE_READWRITE, 0,
                                static_cast<DWORD>(size), NULL);
   if (!section_)
     return NULL;
 
   buffer_ = MapViewOfFile(section_, FILE_MAP_READ | FILE_MAP_WRITE, 0, 0, size);
   DCHECK(buffer_);
   view_size_ = size;
 
   // Make sure we detect hardware failures reading the headers.
-  size_t temp_len = size ? size : 4096;
+  size_t temp_len = size ? size : 4096 * 2;

[gavinp, 2012/05/31 19:59:50]

This is twice as good!  Could we ever have a file less than 8k here?

[rvargas (doing something else), 2012/05/31 20:07:05]

Nope, the header size is 8k.

   scoped_array<char> temp(new char[temp_len]);
   if (!Read(temp.get(), temp_len, 0))
     return NULL;
 
   return buffer_;
 }
 
 MappedFile::~MappedFile() {
   if (!init_)
     return;
@@ skipping 11 matching lines @@
   size_t offset = block->offset() + view_size_;
   return Read(block->buffer(), block->size(), offset);
 }
 
 bool MappedFile::Store(const FileBlock* block) {
   size_t offset = block->offset() + view_size_;
   return Write(block->buffer(), block->size(), offset);
 }
 
 }  // namespace disk_cache