AIO enables even a single application thread to overlap I/O operations with other processing, by providing an interface for submitting one or more I/O requests in one system call (io_submit()) without waiting for completion, and a separate interface (io_getevents()) to reap completed I/O operations associated with a given completion group.
The necessary system calls to support this are included (at least) in the BSP 2.0 kernel provided by Atmel as well as any kernel.org kernel with AVR32 support (i.e. 2.6.19 and later.)
I'm having a hard time finding any "official" web page for the AIO library, so I've attached a tarball to this page which contains the latest libaio1 package from Debian (version 0.3.106-4) with additional support for AVR32.
libaio does not come with a configure script or anything fancy. Simply run
make CC=avr32-linux-gcc ARCH=avr32to build it. You probably need to adjust the prefix variable before installing it.