[poky] Processing extra field requested by bitbake -u in Cache

[Ke, Liping]

Hi, all

I am looking @ bug 770 Add mechanism to enable UI's to request extra data be stored in the cache. We are now thinking about the possible solutions.

There are two choices:
1. Store extra cache fields in a separated small cache file, so non-ui mode will only fetch the base cache file, if in ui-mode, it will load the extra small cache (with the extra 3 fields, such as summary)
  Advantage: 1) Will 'not' change the cache invalidation mechanism. For non-ui mode, it will go the old path. If extra fields are required (ui-mode), we need to load the extra field into the memory.
            2) disk file size is optimized
  Disadvantage: cache code change will be big, since all data load/sync/ methods need to be modified.

2. Have two big cache files, one is for ui mode, one is for non-ui mode
  Advantage: Code change will be a little smaller. When loading, if it's non-ui mode, load smaller cache file. Otherwise, load bigger cache file.  
  Disadvantage: 1) Cache invalidation mechanism (timestamp) is broken. When mode switching, we need to invalidate all caches, reparsing, reloading time 30s.
              s) disk file size is bigger. 2*original_size (2*6M)

Any suggestions?

Thanks a lot for your help!

criping