blkio: add libblkio block driver

libblkio (https://gitlab.com/libblkio/libblkio/) is a library for
high-performance disk I/O. It currently supports io_uring,
virtio-blk-vhost-user, and virtio-blk-vhost-vdpa with additional drivers
under development.

One of the reasons for developing libblkio is that other applications
besides QEMU can use it. This will be particularly useful for
virtio-blk-vhost-user which applications may wish to use for connecting
to qemu-storage-daemon.

libblkio also gives us an opportunity to develop in Rust behind a C API
that is easy to consume from QEMU.

This commit adds io_uring, nvme-io_uring, virtio-blk-vhost-user, and
virtio-blk-vhost-vdpa BlockDrivers to QEMU using libblkio. It will be
easy to add other libblkio drivers since they will share the majority of
code.

For now I/O buffers are copied through bounce buffers if the libblkio
driver requires it. Later commits add an optimization for
pre-registering guest RAM to avoid bounce buffers.

The syntax is:

  --blockdev io_uring,node-name=drive0,filename=test.img,readonly=on|off,cache.direct=on|off

  --blockdev nvme-io_uring,node-name=drive0,filename=/dev/ng0n1,readonly=on|off,cache.direct=on

  --blockdev virtio-blk-vhost-vdpa,node-name=drive0,path=/dev/vdpa...,readonly=on|off,cache.direct=on

  --blockdev virtio-blk-vhost-user,node-name=drive0,path=vhost-user-blk.sock,readonly=on|off,cache.direct=on

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Message-id: 20221013185908.1297568-3-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/meson.build

@@ -92,6 +92,7 @@ block_modules = {}
 
 modsrc = []
 foreach m : [
+  [blkio, 'blkio', files('blkio.c')],
   [curl, 'curl', files('curl.c')],
   [glusterfs, 'gluster', files('gluster.c')],
   [libiscsi, 'iscsi', [files('iscsi.c'), libm]],