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

net/disk_cache/mapped_file_posix.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 <errno.h>
 #include <sys/mman.h>
 
 #include "base/file_path.h"
 #include "base/logging.h"
 #include "net/disk_cache/disk_cache.h"
 
 namespace disk_cache {
 
 void* MappedFile::Init(const FilePath& name, size_t size) {
   DCHECK(!init_);
   if (init_ || !File::Init(name))
     return NULL;
 
   if (!size)
     size = GetLength();
 
   buffer_ = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED,
                  platform_file(), 0);
   init_ = true;
+  view_size_ = size;
   DCHECK(reinterpret_cast<intptr_t>(buffer_) != -1);
   if (reinterpret_cast<intptr_t>(buffer_) == -1)
     buffer_ = 0;
 
-  view_size_ = size;
+  // Make sure we detect hardware failures reading the headers.
+  scoped_array<char> temp(new char[size]);

[gavinp, 2012/06/01 12:00:34]

Now there's another difference with windows.  When size is passed as 0 to the
MappedFile::Init on windows, we just read the 8192 byte header.  But for Posix,
we read the whole file.  Will that slow us down on Posix?

+  if (!Read(temp.get(), size, 0))
+    return NULL;
+
   return buffer_;
 }
 
 bool MappedFile::Load(const FileBlock* block) {
   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);
 }
 
 MappedFile::~MappedFile() {
   if (!init_)
     return;
 
   if (buffer_) {
     int ret = munmap(buffer_, view_size_);
     DCHECK_EQ(0, ret);
   }
 }
 
 }  // namespace disk_cache