RFC preparation for block layer simplification

This is a preparation series for simplifying block layer based on immutable biovecs, a spin off of the v1 of simplifying patchset. [1] The original goal of simplifying block layer was actually making generic_make_request() accept arbitrarily sized bios, and pushing the splitting down to the underlying drivers.

This patchset aims at cleaning up several parts that are independent of core changes in the block layer. Doing that, it could be possible to change block layer relatively easily without keeping up with many patches.

- Patches 01-04/07 do refactoring to make the block layer use the new iov_iter interface.
- Patch 05/07 does refactoring and cleanup in MD-RAID10.
- Patch 06/07 changes a way of refcounting in fs/buffer.c, to be consistent with immutable biovecs API.
- Patch 07/07 makes bio submission in kernel/power in a sane way.

Patches are against 3.19-rc4. These are also available in my git repo at:

https://github.com/dongsupark/linux.git block-prep-simplify

This patchset should be first applied prior to upcoming patchsets such as "simplify block layer based on immutable biovecs." This patchset itself should not bring any regression to end-users.

Comments are welcome.
Dongsu

Changes in v2:
- split up preparation patches from v1 into this separate series.
- In the patch 02, pass iov_iter by value to __bio_copy_iov(), and split into read/write variants, as suggested by Christoph Hellwig.
- minor changes like writing more commit messages etc.

[1] https://lkml.org/lkml/2014/12/22/128

Dongsu Park (1):
block: rewrite __bio_copy_iov()

Kent Overstreet (6):
block: replace sg_iovec with iov_iter
block: refactor iov_count_pages() from bio_{copy,map}_user_iov()
block: refactor bio_get_user_pages() from __bio_map_user_iov() md/raid10: make sync_request_write() call bio_copy_data()
fs: make _submit_bh consistent with generic bio chaining
PM: submit bio in a sane way in cases without bio_chain

 block/bio.c             | 330 +++++++++++++++++++++++++-----------------------
 block/blk-map.c         |  27 ++--
 block/scsi_ioctl.c      |  19 +--
 drivers/md/raid10.c     |  20 +--
 drivers/scsi/sg.c       |  15 +--
 fs/buffer.c             |   4 +-
 include/linux/bio.h     |  10 +-
 include/linux/blkdev.h  |   4 +-
 include/linux/uio.h     |   2 +
 kernel/power/block_io.c |  23 +++-
 lib/iovec.c             |  30 +++++
 11 files changed, 263 insertions(+), 221 deletions(-)

2.1.0