kevent() requires a Vec for its event list, when instead it should probably take a slice

[yorickpeterse]

The wrapper for kevent() is defined as follows:

pub unsafe fn kevent(
    kqueue: impl AsFd,
    changelist: &[Event],
    eventlist: &mut Vec<Event>,
    timeout: Option<Duration>,
) -> io::Result<usize>

Here the eventlist argument is defined as &mut Vec<Event>, requiring a heap allocating of a Vec on every call. For a system where file descriptors are frequently (un)registered (e.g. a busy socket server), it's not unlikely for the Vec allocations to become a bit of a problem.

Would it be possible to change the signature such that eventlist is a &mut [Event] instead? This way one can simply stack allocate the slice, and still use a Vec if deemed necessary (e.g. one is expecting many events).

Some of this was discussed in #578, but it seems nothing was done in response.

[yorickpeterse]

For extra context: I'm porting the network poller setup for https://github.com/inko-lang/inko from the "polling" crate back to direct usage of epoll/kqueue/etc (inko-lang/inko#344 (comment) for more details as to why). Back in ye olde days I used the "nix" crate to interact with kqueue (https://github.com/inko-lang/inko/blob/87b36927d7bd3194e9da90e406f5206d8c713636/vm/src/network_poller/kqueue.rs). Given that I'm already using the rustix crate and long since stopped using the "nix" crate, I'd like to be able to use rustix for this as well, but using a stack allocated array as the old network polling code did.

[oxalica]

I suggest to follow the API of read_uninit and define fn kevent_uninit(&mut [MaybeUninit<Event>], ..) -> Result<(&mut [Event], &mut [MaybeUninit<Event>])>. So we can keep the ability to use uninitialized memory without requiring Vec.