ssize_t readv (int, const struct iovec *, int);
ssize_t writev (int, const struct iovec *, int);
#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
ssize_t preadv (int, const struct iovec *, int, off_t);
ssize_t pwritev (int, const struct iovec *, int, off_t);
ssize_t readv (int, const struct iovec *, int);
ssize_t writev (int, const struct iovec *, int);
#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
ssize_t preadv (int, const struct iovec *, int, off_t);
ssize_t pwritev (int, const struct iovec *, int, off_t);