Add support for vectored registered buffers

Add registered buffer support for vectored io_uring operations. That
allows to pass an iovec, all entries of which must belong to and
point into the same registered buffer specified by sqe->buf_index.

The series covers zerocopy sendmsg and reads / writes. Reads and
writes are implemented as new opcodes, while zerocopy sendmsg
reuses IORING_RECVSEND_FIXED_BUF for the api.

Results are aligned to what one would expect from registered buffers:

t/io_uring + nullblk, single segment 16K:
  34 -> 46 GiB/s
examples/send-zerocopy.c default send size (64KB):
  82558 -> 123855 MB/s

The series is placed on top of 6.15 + zcrx.

Some tests:
https://github.com/isilence/liburing.git regbuf-import

Pavel Begunkov (8):
  io_uring: introduce struct iou_vec
  io_uring: add infra for importing vectored reg buffers
  io_uring/rw: implement vectored registered rw
  io_uring/rw: defer reg buf vec import
  io_uring/net: combine msghdr copy
  io_uring/net: pull vec alloc out of msghdr import
  io_uring/net: convert to struct iou_vec
  io_uring/net: implement vectored reg bufs for zctx

 include/linux/io_uring_types.h |  11 ++
 include/uapi/linux/io_uring.h  |   2 +
 io_uring/alloc_cache.h         |   9 --
 io_uring/net.c                 | 177 ++++++++++++++++++++-------------
 io_uring/net.h                 |   6 +-
 io_uring/opdef.c               |  39 ++++++++
 io_uring/rsrc.c                | 133 +++++++++++++++++++++++++
 io_uring/rsrc.h                |  22 ++++
 io_uring/rw.c                  |  96 ++++++++++++++++--
 io_uring/rw.h                  |   8 +-
 10 files changed, 411 insertions(+), 92 deletions(-)

-- 
2.48.1