io_uring: undeprecate epoll_ctl support

Libuv recently started using it so there is at least one consumer now.

Cc: stable@vger.kernel.org
Fixes: 61a2732af4b0 ("io_uring: deprecate epoll_ctl support")
Link: https://github.com/libuv/libuv/pull/3979
Signed-off-by: Ben Noordhuis <info@bnoordhuis.nl>
Link: https://lore.kernel.org/r/20230506095502.13401-1-info@bnoordhuis.nl
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring: make io_kiocb_to_cmd() typesafe

We need to make sure (at build time) that struct io_cmd_data is not
casted to a structure that's larger.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Link: https://lore.kernel.org/r/c024cdf25ae19fc0319d4180e2298bade8ed17b8.1660201408.git.metze@samba.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring: kill extra io_uring_types.h includes

io_uring/io_uring.h already includes io_uring_types.h, no need to
include it every time. Kill it in a bunch of places, it prepares us for
following patches.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/94d8c943fbe0ef949981c508ddcee7fc1c18850f.1655384063.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring: deprecate epoll_ctl support

As far as we know, nobody ever adopted the epoll_ctl management via
io_uring. Deprecate it now with a warning, and plan on removing it in
a later kernel version. When we do remove it, we can revert the following
commits as well:

39220e8d4a2a ("eventpoll: support non-blocking do_epoll_ctl() calls")
58e41a44c488 ("eventpoll: abstract out epoll_ctl() handler")

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/io-uring/CAHk-=wiTyisXBgKnVHAGYCNvkmjk=50agS2Uk6nr+n3ssLZg2w@mail.gmail.com/
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring: move epoll handler to its own file

Would be nice to sort out Kconfig for this and don't even compile
epoll.c if we don't have epoll configured.

Signed-off-by: Jens Axboe <axboe@kernel.dk>