Function preadv 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn preadv(
    fd: c_int,
    iov: *const iovec,
    iovcnt: c_int,
    offset: off_t,
) -> ssize_t

Non-POSIX, see https://man7.org/linux/man-pages/man2/readv.2.html.

Combines the functionality of readv() and pread().

When successful, returns a non-negative number indicating the number of bytes actually read. Upon failure, returns -1.