o Change the blk_dump_rq_flags() a bit

o Use rq->bio as an indication of ->bio is valid or not, instead of
  checking REQ_PC. Now we can have a bio on a REQ_BLOCK_PC as well.

o Don't print eio error in end_that_request_first(), if REQ_QUIET is set.

o debug check for valid bio in end_that_request_first()

o Add blk_pc_request() check REQ_BLOCK_PC, similar to blk_fs_request()