add more bio helpers v3

[Christoph Hellwig <hch@lst.de>]

Hi all,

this series adds more block layer helpers to remove boilerplate code when
adding memory to a bio or to even do the entire synchronous I/O.

The main aim is to avoid having to convert to a struct page in the caller
when adding kernel direct mapping or vmalloc memory.

Changes since v2:
 - rebase on top of the latest block for-next branch to resolve
   conflicts with the bonuce buffering removal

Changes since v1:
 - typo fixes
 - improve commit messages and kerneldoc comments
 - move bio_add_virt_nofail out of line
 - make the number of bio_vecs calculation helper more generic
 - add another vmalloc helper for the common case

Diffstat:
 block/bio.c                   |  101 +++++++++++++++++++++++++++++++++++++++++
 block/blk-map.c               |   92 +++++++++----------------------------
 drivers/block/pktcdvd.c       |    2 
 drivers/block/rnbd/rnbd-srv.c |    7 --
 drivers/block/ublk_drv.c      |    3 -
 drivers/block/virtio_blk.c    |    4 -
 drivers/md/bcache/super.c     |    3 -
 drivers/md/dm-bufio.c         |    2 
 drivers/md/dm-integrity.c     |   16 ++----
 drivers/nvme/host/core.c      |    2 
 drivers/scsi/scsi_ioctl.c     |    2 
 drivers/scsi/scsi_lib.c       |    3 -
 fs/btrfs/scrub.c              |   10 ----
 fs/gfs2/ops_fstype.c          |   24 +++------
 fs/hfsplus/wrapper.c          |   46 +++---------------
 fs/xfs/xfs_bio_io.c           |   30 ++++--------
 fs/xfs/xfs_buf.c              |   43 +++--------------
 fs/xfs/xfs_log.c              |   32 ++-----------
 fs/zonefs/super.c             |   34 ++++---------
 include/linux/bio.h           |   25 +++++++++-
 include/linux/blk-mq.h        |    4 -
 kernel/power/swap.c           |  103 ++++++++++++++++++------------------------
 22 files changed, 270 insertions(+), 318 deletions(-)