EventFd has no conversion from OwnedFd

[chadaustin]

We pass raw fds into a Rust program via FFI, unix domain sockets, and inheritance. There's no way to use EventFd in those situations because I don't see even an unsafe API to convert OwnedFd into EventFd.

Since it's unsafe, maybe a From instance is not appropriate, but perhaps EventFd::from_fd?

What do you think?

[SteveLauC]

Std implements From<OwnedFd> for almost all the owned fd types, which indeed confuses me. Perhaps we can define a trait like:

pub trait FromOwnedFd {
    unsafe fn from_owned_fd(fd: OwnedFd) -> Self;
}

Just like the FromRawFd trait, does this sound good?

[SteveLauC]

Hmm, given that Nix does not usually define traits (currently, we have only 1 public trait), let's make it a method instead 🫠

impl EventFd {
    unsafe fn from_owned_fd(fd: OwnedFd) -> Self {
        Self(fd)
    }
}