Let me know the verbs which don't have passive voice forms. For example:
He has a pen.(o)
A pen is had by him. (X)
Would you let me know the website about that?
1. He is having dinner.
2. Dinner is being had by him.
(Is #2 correct as a passive voice of #1?)
Technically, #2 is a correct passive of #1, but it's a very awkward sentence. Active is always better if you can do it! Especially with the word "have" or "had" since that word has so many meanings, it's awful!
http://members.cox.net/lenco1/grammarpractice/verbnav.htm
Click on 10. Good, straightforward explanation and examples.
http://grammar.ccc.commnet.edu/grammar/passive.htm <~~good explanation and examples and charts here.
http://owl.english.purdue.edu/owl/
In the right-hand column, click on Grammar and Mechanics and then on Active and Passive Voice.