People were asking about io_uring tx with device memory, this is a quick
and dirty enablement for io_uring's IORING_OP_SEND[MSG]_ZC. It's more of
a testing prototype than to show the design as I'm not happy with uapi
and how it relies on zcrx, and will be redoing it.

It's piggy backed on top of a zcrx instance and relies on it managing
the rx queue and talking to the device. It also uses memory and mappings
from zcrx area. Since there is no proper iter type to pass  netmems,
io_uring gives an ubuf/iovec iterator and relies on a new sg_from_iter
to setup skbs in the right way. Just as devmem TCP, it implmements
{get,put}_netmem by referencing, and verifies in
validate_xmit_unreadable_skb() that skbs go to the right device.

Pavel Begunkov (10):
  net: pass ubuf to custom sg_from_iter callbacks
  net: reject zcrx skbs to not registered devices
  io_uring/zcrx: switch to pcpu refcounting
  io_uring/zcrx: prepare areas to be exported for tx
  io_uring/rsrc: introduce buf registration structure
  io_uring/rsrc: extend buffer update
  io_uring/rsrc: add uncloneable regbuf flag
  io_uring/rsrc: add regbuf import flags
  io_uring/rsrc: add zcrx backed registered buffers
  io_uring/net: implement device memory send

 include/linux/io_uring/net.h  |  10 ++
 include/linux/socket.h        |   2 +-
 include/net/netmem.h          |   1 +
 include/uapi/linux/io_uring.h |  28 ++++-
 io_uring/net.c                |  37 ++++--
 io_uring/notif.h              |   5 +-
 io_uring/rsrc.c               | 204 +++++++++++++++++++++++++++-------
 io_uring/rsrc.h               |  32 +++++-
 io_uring/zcrx.c               | 104 +++++++++++++++--
 io_uring/zcrx.h               |  14 ++-
 net/core/datagram.c           |   2 +-
 net/core/dev.c                |  10 +-
 net/core/skbuff.c             |   3 +
 13 files changed, 381 insertions(+), 71 deletions(-)

-- 
2.54.0