A large part of this article applies just as well to QEMU:
http://lwn.net/SubscriberLink/585782/c50c5822364d5fd5/
Note: The "subscriber link" mechanism allows an LWN.net subscriber to
generate a special URL for a subscription-only article. That URL can
then be given to others, who will be able to access the article
regardless of whether they are subscribed. This feature is made
available as a service to LWN subscribers, and in the hope that they
will use it to spread the word about their favorite LWN articles.
You are more than encouraged to support LWN by subscribing to it!
Thanks,
Paolo