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

net/disk_cache/mapped_file_posix.cc

Index: net/disk_cache/mapped_file_posix.cc
===================================================================
--- net/disk_cache/mapped_file_posix.cc	(revision 138404)
+++ net/disk_cache/mapped_file_posix.cc	(working copy)
@@ -28,6 +28,12 @@
   if (reinterpret_cast<intptr_t>(buffer_) == -1)
     buffer_ = 0;
 
+  // Make sure we detect hardware failures reading the headers.
+  size_t temp_len = size ? size : 4096 * 2;

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

Isn't it just an error if size is 0 here?  How would File::GetLength() return 0,
but we have a file that allows an 8k read without error?

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

Well... that's one of the details that I was hoping you picked when I asked you
to look at this function the other day.

For some reason, it seems to work "as unexpected". We pass 0 all the time,
expecting the whole file to be mapped.

If you think that should be changed, we should do that on a separate CL.

[gavinp, 2012/05/31 20:50:34]

If I missed a request to help earlier, I'm very sorry; but I'm here now!

Passing zero should work; I commented the line up above where it gets filled in,
and why I think the test here is not required.  In the windows version, the test
is needed though.

On 2012/05/31 20:07:05, rvargas wrote:

+  scoped_array<char> temp(new char[temp_len]);
+  if (!Read(temp.get(), temp_len, 0))
+    return NULL;
+
   view_size_ = size;
   return buffer_;
 }