close(raw_fd)—Closes a RawFd directly.
dup(fd)—Creates a new 
OwnedFd instance that shares the same
underlying 
file description as 
fd.
dup3(fd, new, flags)—Changes the 
file description of a file
descriptor, with flags.
fcntl(fd, F_DUPFD_CLOEXEC)—Creates a new OwnedFd instance, with value
at least min, that has O_CLOEXEC set and that shares the same
underlying [file description] as fd.
fcntl(fd, F_GETFD)—Returns a file descriptor’s flags.
fcntl(fd, F_SETFD, flags)—Sets a file descriptor’s flags.
ioctl(fd, FIONBIO, &value)—Enables or disables non-blocking mode.
ioctl(fd, FIONREAD)—Returns the number of bytes ready to be read.
pread(fd, buf, offset)—Reads from a file at a given position.
pread(fd, buf, offset)—Reads from a file at a given position.
preadv(fd, bufs, offset)—Reads from a file at a given position into
multiple buffers.
preadv2(fd, bufs, offset, flags)—Reads data, with several options.
pwrite(fd, bufs)—Writes to a file at a given position.
pwritev(fd, bufs, offset)—Writes to a file at a given position from
multiple buffers.
pwritev2(fd, bufs, offset, flags)—Writes data, with several options.
read(fd, buf)—Reads from a stream.
read(fd, buf)—Reads from a stream.
readv(fd, bufs)—Reads from a stream into multiple buffers.
Call 
f until it either succeeds or fails other than 
Errno::INTR.
write(fd, buf)—Writes to a stream.
writev(fd, bufs)—Writes to a stream from multiple buffers.