virtio: slim down allocation of VirtQueueElements
Build the addresses and s/g lists on the stack, and then copy them to a VirtQueueElement that is just as big as required to contain this particular s/g list. The cost of the copy is minimal compared to that of a large malloc. When virtqueue_map is used on the destination side of migration or on loadvm, the iovecs have already been split at memory region boundary, so we can just reuse the out_num/in_num we find in the file. Reviewed-by: NCornelia Huck <cornelia.huck@de.ibm.com> Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com> Reviewed-by: NMichael S. Tsirkin <mst@redhat.com> Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>
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