ring.cmd_sock is generic socket operation. Two most common uses are
setsockopt and getsockopt. This provides same interface as posix
versions of this methods.
libring has also [sqe_set_flags](https://man7.org/linux/man-pages/man3/io_uring_sqe_set_flags.3.html)
method. Adding that in our io_uring_sqe. Adding sqe.link_next method for setting most common flag.
* io_uring: ring mapped buffers
Ring mapped buffers are newer implementation of ring provided buffers, supported
since kernel 5.19. Best described in Jens Axboe [post](https://github.com/axboe/liburing/wiki/io_uring-and-networking-in-2023#provided-buffers)
This commit implements low level io_uring_*_buf_ring_* functions as mostly
direct translation from liburing. It also adds BufferGroup abstraction over those
low level functions.
* io_uring: add multishot recv to BufferGroup
Once we have ring mapped provided buffers functionality it is possible to use
multishot recv operation. Multishot receive is submitted once, and completions
are posted whenever data arrives on the socket. Received data are placed in a
new buffer from buffer group.
Reference: [io_uring and networking in 2023](https://github.com/axboe/liburing/wiki/io_uring-and-networking-in-2023#multi-shot)
Getting NOENT for cancel completion result, meaning:
-ENOENT
The request identified by user_data could not be located.
This could be because it completed before the cancelation
request was issued, or if an invalid identifier is used.
https://man7.org/linux/man-pages/man3/io_uring_prep_cancel.3.htmlhttps://github.com/ziglang/zig/actions/runs/6801394000/job/18492139893?pr=17806
Result in cancel/recv cqes are different depending on the kernel.
on older kernel (tested with v6.0.16, v6.1.57, v6.2.12, v6.4.16)
cqe_cancel.err() == .NOENT
cqe_crecv.err() == .NOBUFS
on kernel (tested with v6.5.0, v6.5.7)
cqe_cancel.err() == .SUCCESS
cqe_crecv.err() == .CANCELED
* `linux.IO_Uring` -> `linux.IoUring` to align with naming conventions.
* All functions `io_uring_prep_foo` are now methods `prep_foo` on `io_uring_sqe`, which is in a file of its own.
* `SubmissionQueue` and `CompletionQueue` are namespaced under `IoUring`.
This is a breaking change.
The new file and namespace layouts are more idiomatic, and allow us to
eliminate one more usage of `usingnamespace` from the standard library.
2 remain.
