RFC io_uring: prototype for device memory tx

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