In the last set of articles I suggested that barking is really a dog's attempts at the verbal language he hears humans using, or as close to it as the dog can make with his throat. I should have mentioned that this idea of dogs trying to imitate humans is not so fanciful as it might sound. There is a canine behavior that animal behaviorists have said is an imitation of humans. When dogs are around humans they like they will pull back the corners of their mouths. I believe that they do it for humans and not for dogs.
Dogs do sometimes smile as a greeting to humans.
I would like to think that dogs are happy with the pact they have made living with humans. I am not sure because so much of their lives have become boredom. That has to be part of the reason a dog sleeps so much of the time. That means there is much less continuity in how long the day is. A dog wakes up several times a day and probably has a hard time of getting the concept of whether it is morning or afternoon.