System calls preadv(2) and pwritev(2) are provided by Linux kernel, and glibc has wrappers for them, but there are no corresponding man pages. Man pages for pread64(2) and pwrite64(2) redirect to pread(2) man page. However, these system calls aren't mentioned on that man page.
Eugene, this would have been best submitted as two bug reports, because these really are two separate issues. However, by chance, I had recently dealt with on of the issues: the lack of a preadv() and pwritev() documentation (now added to the readv(2) page). Your report triggered me to deal with the other issue as well. I added a note as follows: On Linux, the underlying system calls were renamed in kernel 2.6: pread() became pread64(), and pwrite() became pwrite64(), The system call numbers remained the same. The glibc pread() and pwrite() wrapper functions trans- parently deal with the change. All of the changes are already pushed to git,and will be in man-pages 3.32.