Disk cache: Add a hash to the entry's internal data.

net/disk_cache/disk_format.h

Index: net/disk_cache/disk_format.h
===================================================================
--- net/disk_cache/disk_format.h	(revision 110637)
+++ net/disk_cache/disk_format.h	(working copy)
@@ -123,7 +123,8 @@
   int32       data_size[4];       // We can store up to 4 data streams for each
   CacheAddr   data_addr[4];       // entry.
   uint32      flags;              // Any combination of EntryFlags.
-  int32       pad[5];
+  int32       pad[4];
+  uint32      self_hash;          // The hash of EntryStore up to this point.

[gavinp, 2011/11/29 15:47:42]

Why after the pad, and not before?  What do we expect the pad to usually be?  Is
it because if we later move values out of pad and into use, we'll end up with a
mid-structure self-hash, which would be too confusing?

[rvargas (doing something else), 2011/11/29 19:08:56]

Yes, that's it. Pad is set to zero, and the expected behavior is that we'll want
to verify that whatever we use it for is there. The only reason to not keep
going and hash the key is that we cannot have the hash in the middle of the
stuff that we are hashing (besides, there is already a hash of the key).

   char        key[256 - 24 * 4];  // null terminated
 };
 
@@ -153,7 +154,7 @@
   CacheAddr   prev;             // LRU list.
   CacheAddr   contents;         // Address of the EntryStore.
   int32       dirty;            // The entry is being modifyied.
-  int32       dummy;            // Old files may have a pointer here.
+  uint32      self_hash;        // RankingsNode's hash.
 };
 #pragma pack(pop)