virtio-blk: use generic vectored I/O APIs (Christoph Hellwig) Use the generic bdrv_aio_readv/bdrv_aio_writev APIs instead of linearizing buffers directly. This enables using the future native preadv/pwritev support. Signed-off-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6903 c046a42c-6fe2-441c-8c8c-71466251a162