virtio-blk: avoid g_slice_new0() for VirtIOBlockReq and VirtQueueElement
In commit
de6c8042ec55da18702fa51f09072fcaa315edc3 ("virtio-blk: Avoid
zeroing every request structure") we avoided the 40 KB memset when
allocating VirtIOBlockReq.
The memset was reintroduced in commit
671ec3f056559f22a2531a91dce3a258b9b5eb8a ("virtio-blk: Convert
VirtIOBlockReq.elem to pointer").
It must be fixed again to avoid a performance regression.
Cc: Fam Zheng <famz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>