Re: Buffer state bits

BH_Mapped
- Buffer has a physical block backing it stored in b_bdev + b_blocknr. This bit
  is set by filesystem's get_block() function (or by VFS itself for block device
  mappings).

  XXX: Some filesystems set BH_Mapped even for buffers that do no really
  have the backing block (like buffers for delayed allocation). I think
  we should get rid of it...

Also we don't want get_block to be called multiple times for the same file offset.
__block_prepare_write does get_block looking at the BH_Mapped flag. ie one of reason
delay and unwritten buffer_heads are also marked mapped.


-aneesh