Hi,
Interests[1] have been shown in multipage bvecs, so this patchset
try to prepare for the support and do two things:
1) the 1st 4 patches use bvec iterator to implement iterate_bvec(),
then we can drop the non-standard way for iterating bvec, which
can be thought as a good cleanup for lib/iov_iter.c
2) remove BIO_MAX_SECTORS & BIO_MAX_SIZE, and now there is only
one user for each. Once multipage bvecs is introduced, one bio
may hold lots of sectors, and we should always use sort of BIO_MAX_VECS
which should be introduced in future and is similiar with current
BIO_MAX_PAGES.
xfstests(-a auto) have been run over ext4/xfs and no regression found
by this patchset.