Has been always a small personal challenge to find a comfortable position for eating... I am surely not a master of skill and elasticity to stay in that position for more than two minutes. Strategically speaking people prefered to get a place as closer as possible to the small kitchen, where these buckets full of food were coming from. My personal strategy instead was to find a place where there was at least one column to support my back.
More or less to eat a meal you have 10 minutes, before another horde of hungry people pour into the room. What you have to do (besides eating) is simply wait one of these characters with the bucket. These people run constantly between the rows created by the people sitting.. Normally there are three different types of food inside... you just have to say yes or not, and they will pour it on your plate as often as you like.
What you see photographed is the famous "Dal" .. a sauce made with lentils. Then there was usually something made from potatoes (aloo), and the porridge.
Vegetarian food... cook meat for all these people would have been pretty onerous for costs and fatigue.