Hi,

The attached patch adds preadv and pwritev system calls.  These syscalls
are a pretty straightforward combination of pread and readv (same for
write).  They are quite useful for doing vectored I/O in threaded
applications.  Using lseek+readv instead opens race windows you'll have
to plug with locking.

Other systems have such system calls too, for example NetBSD, check
here: http://www.daemon-systems.org/man/preadv.2.html

The patch sports the actual system call implementation and the windup in
the x86 system call tables.  Other archs are TBD.

Comments?  Reviews?  Suggestions?  Flames?

cheers,
  Gerd