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    use {Error, Result, NixPath};
    use errno::Errno;
    use libc::{self, c_int, c_uint, c_char, size_t, ssize_t};
    use sys::stat::Mode;
    use std::os::raw;
    use std::os::unix::io::RawFd;
    use std::ffi::OsStr;
    use std::os::unix::ffi::OsStrExt;

    #[cfg(any(target_os = "android", target_os = "linux"))]
    use sys::uio::IoVec;  // For vmsplice

    libc_bitflags!{
        pub struct AtFlags: c_int {
            AT_SYMLINK_NOFOLLOW;
            #[cfg(any(target_os = "android", target_os = "linux"))]
            AT_NO_AUTOMOUNT;
            #[cfg(any(target_os = "android", target_os = "linux"))]
            AT_EMPTY_PATH;
        }
    }

    libc_bitflags!(
        /// Configuration options for opened files.
        pub struct OFlag: c_int {
            /// Mask for the access mode of the file.
            O_ACCMODE;
            /// Use alternate I/O semantics.
            #[cfg(target_os = "netbsd")]
            O_ALT_IO;
            /// Open the file in append-only mode.
            O_APPEND;
            /// Generate a signal when input or output becomes possible.
            O_ASYNC;
            /// Closes the file descriptor once an `execve` call is made.
            ///
            /// Also sets the file offset to the beginning of the file.
            O_CLOEXEC;
            /// Create the file if it does not exist.
            O_CREAT;
            /// Try to minimize cache effects of the I/O for this file.
            #[cfg(any(target_os = "android",
                      target_os = "dragonfly",
                      target_os = "freebsd",
                      target_os = "linux",
                      target_os = "netbsd"))]
            O_DIRECT;
            /// If the specified path isn't a directory, fail.
            O_DIRECTORY;
            /// Implicitly follow each `write()` with an `fdatasync()`.
            #[cfg(any(target_os = "android",
                      target_os = "ios",
                      target_os = "linux",
                      target_os = "macos",
                      target_os = "netbsd",
                      target_os = "openbsd"))]
            O_DSYNC;
            /// Error out if a file was not created.
            O_EXCL;
            /// Open for execute only.
            #[cfg(target_os = "freebsd")]
            O_EXEC;
            /// Open with an exclusive file lock.
            #[cfg(any(target_os = "dragonfly",
                      target_os = "freebsd",
                      target_os = "ios",
                      target_os = "macos",
                      target_os = "netbsd",
                      target_os = "openbsd"))]
            O_EXLOCK;
            /// Same as `O_SYNC`.
            #[cfg(any(target_os = "dragonfly",
                      target_os = "freebsd",
                      target_os = "ios",
                      all(target_os = "linux", not(target_env = "musl")),
                      target_os = "macos",
                      target_os = "netbsd",
                      target_os = "openbsd"))]
            O_FSYNC;
            /// Allow files whose sizes can't be represented in an `off_t` to be opened.
            #[cfg(any(target_os = "android", target_os = "linux"))]
            O_LARGEFILE;
            /// Do not update the file last access time during `read(2)`s.
            #[cfg(any(target_os = "android", target_os = "linux"))]
            O_NOATIME;
            /// Don't attach the device as the process' controlling terminal.
            O_NOCTTY;
            /// Same as `O_NONBLOCK`.
            O_NDELAY;
            /// `open()` will fail if the given path is a symbolic link.
            O_NOFOLLOW;
            /// When possible, open the file in nonblocking mode.
            O_NONBLOCK;
            /// Don't deliver `SIGPIPE`.
            #[cfg(target_os = "netbsd")]
            O_NOSIGPIPE;
            /// Obtain a file descriptor for low-level access.
            ///
            /// The file itself is not opened and other file operations will fail.
            #[cfg(any(target_os = "android", target_os = "linux"))]
            O_PATH;
            /// Only allow reading.
            ///
            /// This should not be combined with `O_WRONLY` or `O_RDWR`.
            O_RDONLY;
            /// Allow both reading and writing.
            ///
            /// This should not be combined with `O_WRONLY` or `O_RDONLY`.
            O_RDWR;
            /// Similar to `O_DSYNC` but applies to `read`s instead.
            #[cfg(any(target_os = "linux", target_os = "netbsd", target_os = "openbsd"))]
            O_RSYNC;
            /// Skip search permission checks.
            #[cfg(target_os = "netbsd")]
            O_SEARCH;
            /// Open with a shared file lock.
            #[cfg(any(target_os = "dragonfly",
                      target_os = "freebsd",
                      target_os = "ios",
                      target_os = "macos",
                      target_os = "netbsd",
                      target_os = "openbsd"))]
            O_SHLOCK;
            /// Implicitly follow each `write()` with an `fsync()`.
            O_SYNC;
            /// Create an unnamed temporary file.
            #[cfg(any(target_os = "android", target_os = "linux"))]
            O_TMPFILE;
            /// Truncate an existing regular file to 0 length if it allows writing.
            O_TRUNC;
            /// Restore default TTY attributes.
            #[cfg(target_os = "freebsd")]
            O_TTY_INIT;
            /// Only allow writing.
            ///
            /// This should not be combined with `O_RDONLY` or `O_RDWR`.
            O_WRONLY;
        }
    );

    pub fn open<P: ?Sized + NixPath>(path: &P, oflag: OFlag, mode: Mode) -> Result<RawFd> {
        let fd = path.with_nix_path(|cstr| {
            unsafe { libc::open(cstr.as_ptr(), oflag.bits(), mode.bits() as c_uint) }
        })?;

        Errno::result(fd)
    }

    pub fn openat<P: ?Sized + NixPath>(dirfd: RawFd, path: &P, oflag: OFlag, mode: Mode) -> Result<RawFd> {
        let fd = path.with_nix_path(|cstr| {
            unsafe { libc::openat(dirfd, cstr.as_ptr(), oflag.bits(), mode.bits() as c_uint) }
        })?;
        Errno::result(fd)
    }

    fn wrap_readlink_result(buffer: &mut[u8], res: ssize_t) -> Result<&OsStr> {
        match Errno::result(res) {
            Err(err) => Err(err),
            Ok(len) => {
                if (len as usize) >= buffer.len() {
                    Err(Error::Sys(Errno::ENAMETOOLONG))
                } else {
                    Ok(OsStr::from_bytes(&buffer[..(len as usize)]))
                }
            }
        }
    }

    pub fn readlink<'a, P: ?Sized + NixPath>(path: &P, buffer: &'a mut [u8]) -> Result<&'a OsStr> {
        let res = path.with_nix_path(|cstr| {
            unsafe { libc::readlink(cstr.as_ptr(), buffer.as_mut_ptr() as *mut c_char, buffer.len() as size_t) }
        })?;

        wrap_readlink_result(buffer, res)
    }

    pub fn readlinkat<'a, P: ?Sized + NixPath>(dirfd: RawFd, path: &P, buffer: &'a mut [u8]) -> Result<&'a OsStr> {
        let res = path.with_nix_path(|cstr| {
            unsafe { libc::readlinkat(dirfd, cstr.as_ptr(), buffer.as_mut_ptr() as *mut c_char, buffer.len() as size_t) }
        })?;

        wrap_readlink_result(buffer, res)
    }

    /// Computes the raw fd consumed by a function of the form `*at`.
    pub(crate) fn at_rawfd(fd: Option<RawFd>) -> raw::c_int {
        match fd {
            None => libc::AT_FDCWD,
            Some(fd) => fd,
        }
    }

    #[cfg(any(target_os = "android", target_os = "linux"))]
    libc_bitflags!(
        /// Additional flags for file sealing, which allows for limiting operations on a file.
        pub struct SealFlag: c_int {
            /// Prevents further calls to `fcntl()` with `F_ADD_SEALS`.
            F_SEAL_SEAL;
            /// The file cannot be reduced in size.
            F_SEAL_SHRINK;
            /// The size of the file cannot be increased.
            F_SEAL_GROW;
            /// The file contents cannot be modified.
            F_SEAL_WRITE;
        }
    );

    libc_bitflags!(
        /// Additional configuration flags for `fcntl`'s `F_SETFD`.
        pub struct FdFlag: c_int {
            /// The file descriptor will automatically be closed during a successful `execve(2)`.
            FD_CLOEXEC;
        }
    );

    #[allow(missing_debug_implementations)]
    pub enum FcntlArg<'a> {
        F_DUPFD(RawFd),
        F_DUPFD_CLOEXEC(RawFd),
        F_GETFD,
        F_SETFD(FdFlag), // FD_FLAGS
        F_GETFL,
        F_SETFL(OFlag), // O_NONBLOCK
        F_SETLK(&'a libc::flock),
        F_SETLKW(&'a libc::flock),
        F_GETLK(&'a mut libc::flock),
        #[cfg(any(target_os = "linux", target_os = "android"))]
        F_OFD_SETLK(&'a libc::flock),
        #[cfg(any(target_os = "linux", target_os = "android"))]
        F_OFD_SETLKW(&'a libc::flock),
        #[cfg(any(target_os = "linux", target_os = "android"))]
        F_OFD_GETLK(&'a mut libc::flock),
        #[cfg(any(target_os = "android", target_os = "linux"))]
        F_ADD_SEALS(SealFlag),
        #[cfg(any(target_os = "android", target_os = "linux"))]
        F_GET_SEALS,
        #[cfg(any(target_os = "macos", target_os = "ios"))]
        F_FULLFSYNC,
        #[cfg(any(target_os = "linux", target_os = "android"))]
        F_GETPIPE_SZ,
        #[cfg(any(target_os = "linux", target_os = "android"))]
        F_SETPIPE_SZ(c_int),

        // TODO: Rest of flags
    }
    pub use self::FcntlArg::*;

    // TODO: Figure out how to handle value fcntl returns
    pub fn fcntl(fd: RawFd, arg: FcntlArg) -> Result<c_int> {
        let res = unsafe {
            match arg {
                F_DUPFD(rawfd) => libc::fcntl(fd, libc::F_DUPFD, rawfd),
                F_DUPFD_CLOEXEC(rawfd) => libc::fcntl(fd, libc::F_DUPFD_CLOEXEC, rawfd),
                F_GETFD => libc::fcntl(fd, libc::F_GETFD),
                F_SETFD(flag) => libc::fcntl(fd, libc::F_SETFD, flag.bits()),
                F_GETFL => libc::fcntl(fd, libc::F_GETFL),
                F_SETFL(flag) => libc::fcntl(fd, libc::F_SETFL, flag.bits()),
                F_SETLK(flock) => libc::fcntl(fd, libc::F_SETLK, flock),
                F_SETLKW(flock) => libc::fcntl(fd, libc::F_SETLKW, flock),
                F_GETLK(flock) => libc::fcntl(fd, libc::F_GETLK, flock),
                #[cfg(any(target_os = "android", target_os = "linux"))]
                F_ADD_SEALS(flag) => libc::fcntl(fd, libc::F_ADD_SEALS, flag.bits()),
                #[cfg(any(target_os = "android", target_os = "linux"))]
                F_GET_SEALS => libc::fcntl(fd, libc::F_GET_SEALS),
                #[cfg(any(target_os = "macos", target_os = "ios"))]
                F_FULLFSYNC => libc::fcntl(fd, libc::F_FULLFSYNC),
                #[cfg(any(target_os = "linux", target_os = "android"))]
                F_GETPIPE_SZ => libc::fcntl(fd, libc::F_GETPIPE_SZ),
                #[cfg(any(target_os = "linux", target_os = "android"))]
                F_SETPIPE_SZ(size) => libc::fcntl(fd, libc::F_SETPIPE_SZ, size),
                #[cfg(any(target_os = "linux", target_os = "android"))]
                _ => unimplemented!()
            }
        };

        Errno::result(res)
    }

    #[derive(Clone, Copy)]
    #[allow(missing_debug_implementations)]
    pub enum FlockArg {
        LockShared,
        LockExclusive,
        Unlock,
        LockSharedNonblock,
        LockExclusiveNonblock,
        UnlockNonblock,
    }

    pub fn flock(fd: RawFd, arg: FlockArg) -> Result<()> {
        use self::FlockArg::*;

        let res = unsafe {
            match arg {
                LockShared => libc::flock(fd, libc::LOCK_SH),
                LockExclusive => libc::flock(fd, libc::LOCK_EX),
                Unlock => libc::flock(fd, libc::LOCK_UN),
                LockSharedNonblock => libc::flock(fd, libc::LOCK_SH | libc::LOCK_NB),
                LockExclusiveNonblock => libc::flock(fd, libc::LOCK_EX | libc::LOCK_NB),
                UnlockNonblock => libc::flock(fd, libc::LOCK_UN | libc::LOCK_NB),
            }
        };

        Errno::result(res).map(drop)
    }

    #[cfg(any(target_os = "android", target_os = "linux"))]
    libc_bitflags! {
        /// Additional flags to `splice` and friends.
        pub struct SpliceFFlags: c_uint {
            /// Request that pages be moved instead of copied.
            ///
            /// Not applicable to `vmsplice`.
            SPLICE_F_MOVE;
            /// Do not block on I/O.
            SPLICE_F_NONBLOCK;
            /// Hint that more data will be coming in a subsequent splice.
            ///
            /// Not applicable to `vmsplice`.
            SPLICE_F_MORE;
            /// Gift the user pages to the kernel.
            ///
            /// Not applicable to `splice`.
            SPLICE_F_GIFT;
        }
    }

    #[cfg(any(target_os = "linux", target_os = "android"))]
    pub fn splice(fd_in: RawFd, off_in: Option<&mut libc::loff_t>,
              fd_out: RawFd, off_out: Option<&mut libc::loff_t>,
              len: usize, flags: SpliceFFlags) -> Result<usize> {
        use std::ptr;
        let off_in = off_in.map(|offset| offset as *mut _).unwrap_or(ptr::null_mut());
        let off_out = off_out.map(|offset| offset as *mut _).unwrap_or(ptr::null_mut());

        let ret = unsafe { libc::splice(fd_in, off_in, fd_out, off_out, len, flags.bits()) };
        Errno::result(ret).map(|r| r as usize)
    }

    #[cfg(any(target_os = "linux", target_os = "android"))]
    pub fn tee(fd_in: RawFd, fd_out: RawFd, len: usize, flags: SpliceFFlags) -> Result<usize> {
        let ret = unsafe { libc::tee(fd_in, fd_out, len, flags.bits()) };
        Errno::result(ret).map(|r| r as usize)
    }

    #[cfg(any(target_os = "linux", target_os = "android"))]
    pub fn vmsplice(fd: RawFd, iov: &[IoVec<&[u8]>], flags: SpliceFFlags) -> Result<usize> {
        let ret = unsafe {
            libc::vmsplice(fd, iov.as_ptr() as *const libc::iovec, iov.len(), flags.bits())
        };
        Errno::result(ret).map(|r| r as usize)
    }

    #[cfg(any(target_os = "linux"))]
    libc_bitflags!(
        /// Mode argument flags for fallocate determining operation performed on a given range.
        pub struct FallocateFlags: c_int {
            /// File size is not changed.
            ///
            /// offset + len can be greater than file size.
            FALLOC_FL_KEEP_SIZE;
            /// Deallocates space by creating a hole.
            ///
            /// Must be ORed with FALLOC_FL_KEEP_SIZE. Byte range starts at offset and continues for len bytes.
            FALLOC_FL_PUNCH_HOLE;
            /// Removes byte range from a file without leaving a hole.
            ///
            /// Byte range to collapse starts at offset and continues for len bytes.
            FALLOC_FL_COLLAPSE_RANGE;
            /// Zeroes space in specified byte range.
            ///
            /// Byte range starts at offset and continues for len bytes.
            FALLOC_FL_ZERO_RANGE;
            /// Increases file space by inserting a hole within the file size.
            ///
            /// Does not overwrite existing data. Hole starts at offset and continues for len bytes.
            FALLOC_FL_INSERT_RANGE;
            /// Shared file data extants are made private to the file.
            ///
            /// Gaurantees that a subsequent write will not fail due to lack of space.
            FALLOC_FL_UNSHARE_RANGE;
        }
    );

    /// Manipulates file space.
    ///
    /// Allows the caller to directly manipulate the allocated disk space for the
    /// file referred to by fd.
    #[cfg(any(target_os = "linux"))]
    pub fn fallocate(fd: RawFd, mode: FallocateFlags, offset: libc::off_t, len: libc::off_t) -> Result<c_int> {
        let res = unsafe { libc::fallocate(fd, mode.bits(), offset, len) };
        Errno::result(res)
    }

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