start adding the tag to iov_iter

For now, just use the same thing we pass to ->direct_IO() - it's all
iovec-based at the moment.  Pass it explicitly to iov_iter_init() and
account for kvec vs. iovec in there, by the same kludge NFS ->direct_IO()
uses.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc fs/btrfs/file.c
Simple merge

diff --cc fs/ceph/file.c
Simple merge

diff --cc fs/cifs/file.c
Simple merge

diff --cc fs/fuse/file.c
Simple merge

diff --cc fs/nfs/file.c
Simple merge

diff --cc fs/ocfs2/file.c
Simple merge

diff --cc fs/pipe.c
Simple merge

diff --cc fs/splice.c
Simple merge

diff --cc fs/xfs/xfs_file.c
Simple merge

diff --cc include/linux/uio.h
Simple merge

diff --cc mm/filemap.c
Simple merge

diff --cc mm/iov_iter.c
Simple merge

diff --cc mm/page_io.c
Simple merge

diff --cc mm/process_vm_access.c
Simple merge

diff --cc mm/shmem.c
Simple merge