block & iov_iter: use bvec iterator to implement iterate_bvec()

[Ming Lei]

Hi Guys,

The 1st two patches move bvec iterator helpers out from bio.h, then
they can be used even if CONFIG_BLOCK is disabled, so not necessary
to use iov iter own approach to do the job.

One motivation is that in the future we may support multipage bvecs,
as interests[1] have been shown in this idea, so looks better to
unify the implementation now.

[1], http://marc.info/?w=2&r=1&s=++[LSF%2FMM+ATTEND]+block%3A+multipage+bvecs&q=t
 

 include/linux/bio.h       | 55 +------------------------------------------
 include/linux/blk_types.h |  4 ++--
 include/linux/bvec_iter.h | 79 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 lib/iov_iter.c            | 31 +++++++++---------------
 4 files changed, 93 insertions(+), 76 deletions(-)


Thanks,
Ming