Return true when file size is zero.

base/test/test_file_util_mac.cc

 // Copyright (c) 2008 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/test/test_file_util.h"
 
 #include <sys/mman.h>
 #include <errno.h>
 #include "base/logging.h"
 #include "base/file_util.h"
 
 namespace file_util {
 
 bool EvictFileFromSystemCache(const FilePath& file) {
   // There aren't any really direct ways to purge a file from the UBC.  From
   // talking with Amit Singh, the safest is to mmap the file with MAP_FILE (the
   // default) + MAP_SHARED, then do an msync to invalidate the memory.  The next
   // open should then have to load the file from disk.
 
+  int64 length;
+  if (!file_util::GetFileSize(file, &length)) {

[kkania, 2011/07/23 00:27:02]

now that I think about it, I'm not sure this is correct. If you don't evict from
the cache and the file changes, will later reads possibly still see the empty
file? Or is an empty file not in the cache to begin with?

[TVL, 2011/07/25 12:40:10]

If the OS cache had that sort of bugs/behaviors, you can assume all sorts of
things would probably go wrong.  In this case, since the file is zero sized,
there really isn't anything for it to have cached.

+    DLOG(WARNING) << "failed to get size of " << file.value();
+    return false;
+  }
+
+  // When a file is empty, we do not need to purge it.

[kkania, 2011/07/23 00:23:31]

maybe include that mapping it would cause an error?

+  if (!length)
+    return true;
+
   file_util::MemoryMappedFile mapped_file;
   if (!mapped_file.Initialize(file)) {
     DLOG(WARNING) << "failed to memory map " << file.value();
     return false;
   }
 
   if (msync(const_cast<uint8*>(mapped_file.data()), mapped_file.length(),
             MS_INVALIDATE) != 0) {
     DLOG(WARNING) << "failed to invalidate memory map of " << file.value()
         << ", errno: " << errno;
     return false;
   }
 
   return true;
 }
 
 }  // namespace file_util