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    //! `read` and `write`, optionally positioned, optionally vectored

    use crate::{backend, io};
    use backend::fd::AsFd;

    // Declare `IoSlice` and `IoSliceMut`.
    #[cfg(not(windows))]
    #[cfg(not(feature = "std"))]
    pub use backend::io::io_slice::{IoSlice, IoSliceMut};
    #[cfg(not(windows))]
    #[cfg(feature = "std")]
    pub use std::io::{IoSlice, IoSliceMut};

    /// `RWF_*` constants for use with [`preadv2`] and [`pwritev2`].
    #[cfg(any(target_os = "android", target_os = "linux"))]
    pub use backend::io::types::ReadWriteFlags;

    /// `read(fd, buf)`—Reads from a stream.
    ///
    /// # References
    ///  - [POSIX]
    ///  - [Linux]
    ///  - [Apple]
    ///
    /// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/read.html
    /// [Linux]: https://man7.org/linux/man-pages/man2/read.2.html
    /// [Apple]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/read.2.html
    #[inline]
    pub fn read<Fd: AsFd>(fd: Fd, buf: &mut [u8]) -> io::Result<usize> {
        backend::io::syscalls::read(fd.as_fd(), buf)
    }

    /// `write(fd, buf)`—Writes to a stream.
    ///
    /// # References
    ///  - [POSIX]
    ///  - [Linux]
    ///  - [Apple]
    ///
    /// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/write.html
    /// [Linux]: https://man7.org/linux/man-pages/man2/write.2.html
    /// [Apple]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/write.2.html
    #[inline]
    pub fn write<Fd: AsFd>(fd: Fd, buf: &[u8]) -> io::Result<usize> {
        backend::io::syscalls::write(fd.as_fd(), buf)
    }

    /// `pread(fd, buf, offset)`—Reads from a file at a given position.
    ///
    /// # References
    ///  - [POSIX]
    ///  - [Linux]
    ///  - [Apple]
    ///
    /// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/pread.html
    /// [Linux]: https://man7.org/linux/man-pages/man2/pread.2.html
    /// [Apple]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/pread.2.html
    #[inline]
    pub fn pread<Fd: AsFd>(fd: Fd, buf: &mut [u8], offset: u64) -> io::Result<usize> {
        backend::io::syscalls::pread(fd.as_fd(), buf, offset)
    }

    /// `pwrite(fd, bufs)`—Writes to a file at a given position.
    ///
    /// Contrary to POSIX, on many popular platforms including Linux and FreeBSD,
    /// if the file is opened in append mode, this ignores the offset appends the
    /// data to the end of the file.
    ///
    /// # References
    ///  - [POSIX]
    ///  - [Linux]
    ///  - [Apple]
    ///
    /// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/pwrite.html
    /// [Linux]: https://man7.org/linux/man-pages/man2/pwrite.2.html
    /// [Apple]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/pwrite.2.html
    #[inline]
    pub fn pwrite<Fd: AsFd>(fd: Fd, buf: &[u8], offset: u64) -> io::Result<usize> {
        backend::io::syscalls::pwrite(fd.as_fd(), buf, offset)
    }

    /// `readv(fd, bufs)`—Reads from a stream into multiple buffers.
    ///
    /// # References
    ///  - [POSIX]
    ///  - [Linux]
    ///  - [Apple]
    ///
    /// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/readv.html
    /// [Linux]: https://man7.org/linux/man-pages/man2/readv.2.html
    /// [Apple]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/readv.2.html
    #[inline]
    pub fn readv<Fd: AsFd>(fd: Fd, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        backend::io::syscalls::readv(fd.as_fd(), bufs)
    }

    /// `writev(fd, bufs)`—Writes to a stream from multiple buffers.
    ///
    /// # References
    ///  - [POSIX]
    ///  - [Linux]
    ///  - [Apple]
    ///
    /// [POSIX]: https://pubs.opengroup.org/onlinepubs/9699919799/functions/writev.html
    /// [Linux]: https://man7.org/linux/man-pages/man2/writev.2.html
    /// [Apple]: https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/writev.2.html
    #[inline]
    pub fn writev<Fd: AsFd>(fd: Fd, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        backend::io::syscalls::writev(fd.as_fd(), bufs)
    }

    /// `preadv(fd, bufs, offset)`—Reads from a file at a given position into
    /// multiple buffers.
    ///
    /// # References
    ///  - [Linux]
    ///
    /// [Linux]: https://man7.org/linux/man-pages/man2/preadv.2.html
    #[cfg(not(any(target_os = "haiku", target_os = "redox", target_os = "solaris")))]
    #[inline]
    pub fn preadv<Fd: AsFd>(fd: Fd, bufs: &mut [IoSliceMut<'_>], offset: u64) -> io::Result<usize> {
        backend::io::syscalls::preadv(fd.as_fd(), bufs, offset)
    }

    /// `pwritev(fd, bufs, offset)`—Writes to a file at a given position from
    /// multiple buffers.
    ///
    /// Contrary to POSIX, on many popular platforms including Linux and FreeBSD,
    /// if the file is opened in append mode, this ignores the offset appends the
    /// data to the end of the file.
    ///
    /// # References
    ///  - [Linux]
    ///
    /// [Linux]: https://man7.org/linux/man-pages/man2/pwritev.2.html
    #[cfg(not(any(target_os = "haiku", target_os = "redox", target_os = "solaris")))]
    #[inline]
    pub fn pwritev<Fd: AsFd>(fd: Fd, bufs: &[IoSlice<'_>], offset: u64) -> io::Result<usize> {
        backend::io::syscalls::pwritev(fd.as_fd(), bufs, offset)
    }

    /// `preadv2(fd, bufs, offset, flags)`—Reads data, with several options.
    ///
    /// An `offset` of `u64::MAX` means to use and update the current file offset.
    ///
    /// # References
    ///  - [Linux]
    ///
    /// [Linux]: https://man7.org/linux/man-pages/man2/preadv2.2.html
    #[cfg(any(target_os = "android", target_os = "linux"))]
    #[inline]
    pub fn preadv2<Fd: AsFd>(
        fd: Fd,
        bufs: &mut [IoSliceMut<'_>],
        offset: u64,
        flags: ReadWriteFlags,
    ) -> io::Result<usize> {
        backend::io::syscalls::preadv2(fd.as_fd(), bufs, offset, flags)
    }

    /// `pwritev2(fd, bufs, offset, flags)`—Writes data, with several options.
    ///
    /// An `offset` of `u64::MAX` means to use and update the current file offset.
    ///
    /// # References
    ///  - [Linux]
    ///
    /// [Linux]: https://man7.org/linux/man-pages/man2/pwritev2.2.html
    #[cfg(any(target_os = "android", target_os = "linux"))]
    #[inline]
    pub fn pwritev2<Fd: AsFd>(
        fd: Fd,
        bufs: &[IoSlice<'_>],
        offset: u64,
        flags: ReadWriteFlags,
    ) -> io::Result<usize> {
        backend::io::syscalls::pwritev2(fd.as_fd(), bufs, offset, flags)
    }