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use std::os::unix::io::RawFd;
use linux_io_uring_sys as sys;

/// Register files or user buffers for asynchronous I/O.
#[allow(clippy::module_inception)]
pub mod register {
    use super::*;

    pub enum Target<'a> {
        /// Register buffer,
        /// then use the already registered buffer in
        /// [ReadFixed](crate::opcode::ReadFixed) and [WriteFixed](crate::opcode::WriteFixed).
        Buffer(&'a [libc::iovec]),

        /// Register file descriptor,
        /// then use the already registered fd in [Target::Fixed](crate::opcode::Target).
        File(&'a [RawFd]),

        /// Register eventfd.
        Event(RawFd),

        // TODO https://github.com/rust-lang/rust/pull/64639
        #[doc(hidden)]
        __Unknown
    }

    impl Target<'_> {
        pub(crate) fn export(&self) -> (libc::c_uint, *const libc::c_void, libc::c_uint) {
            fn cast_ptr<T>(n: &T) -> *const T {
                n as *const T
            }

            match self {
                Target::Buffer(bufs) =>
                    (sys::IORING_REGISTER_BUFFERS, bufs.as_ptr() as *const _, bufs.len() as _),
                Target::File(fds) =>
                    (sys::IORING_REGISTER_FILES, fds.as_ptr() as *const _, fds.len() as _),
                Target::Event(eventfd)
                    => (sys::IORING_REGISTER_EVENTFD, cast_ptr::<RawFd>(eventfd) as *const _, 1),
                _ => unreachable!()
            }
        }
    }
}

/// Unregister files or user buffers for asynchronous I/O.
pub mod unregister {
    use super::*;

    pub enum Target {
        /// Unregister buffer.
        Buffer,

        /// Unregister file descriptor.
        File,

        /// Unregister eventfd.
        Event,

        #[doc(hidden)]
        __Unknown
    }

    impl Target {
        pub(crate) fn opcode(&self) -> libc::c_uint {
            match self {
                Target::Buffer => sys::IORING_UNREGISTER_BUFFERS,
                Target::File => sys::IORING_UNREGISTER_FILES,
                Target::Event => sys::IORING_UNREGISTER_EVENTFD,
                _ => unreachable!()
            }
        }
    }
}