RFC zcrx mapping cleanups and device-less instances

First two patches move user memory DMA map creation to an earlier point, which makes it more uniform among different memory types and easier to manage. Patches 3 and 4 introduce device-less zcrx instances for testing purposes, which always copy data via the fallback path.

note, based on two other recently sent patches splitting out a uapi file and defining constants in zcrx.h

Pavel Begunkov (4):
io_uring/zcrx: fully clean area on error in io_import_umem() io_uring/zcrx: always dma map in advance io_uring/zcrx: extract netdev+area init into a helper io_uring/zcrx: implement device-less mode for zcrx

 include/uapi/linux/io_uring/zcrx.h |   9 +-
 io_uring/zcrx.c                    | 145 ++++++++++++++++-------------
 io_uring/zcrx.h                    |   2 +-
 3 files changed, 90 insertions(+), 66 deletions(-)

2.52.0