Not sure where gregorz is going with announcing that, but each to their own...
So, we'll be doing exactly this this year. With 3 vague principles:
1) if veg doesn't enter the house... so goes straight from field to pig, then it's legal food, as far as I understand it.
2) roots are a good staple, and can usually be bought by the tonne from a local supplier
3) barley meal used to be a staple pig food for people who didn't use swill. Barley meal is basically a course ground barley flour, which is mixed with water and fed to the pigs. This would be the bulk of food, supplemented by items 1) and 2) to add variety and trace elements.
Lots and lots of care needed to ensure they don't run to fat.... but once you've got the measurements right, it's easy.
I've consulted pretty widely on this (Not on the internet so much).
The trouble with places like this is that you don't get many 80 year old farmers on here... that period of animals husbandry before imported soy and engineered feed has a lot to tell us about how to keep animals.