Overall, I would say that Santiago's father acted calmly.  He didn't get angry or abusive.  He didn't start yelling at his son.  He didn't get insulting, nor did he "put his foot down" and mandate that Santiago stay at home and become a priest.  

Santiago's father calmly entered into the conversation by pointing out that when people visit their part of the world, they say it is beautiful and don't want to leave.  He asks Santiago why he would want to leave a place that is so desirable.  

"Those people, when they see our land, say that they would like to live here forever," his father continued.

Santiago is undeterred and responds by saying that he still wants to go.  The father calmly points out that it will take a lot of money, which Santiago doesn't have.   

"The people who come here have a lot of money to spend, so they can afford to travel," his father said.

Santiago is still determined to travel.  The next day, despite not wanting his son to leave, the father gave Santiago a pouch of coins to help him travel. He also gave Santiago his blessing. 

Santiago's family wanted him to be a priest, and so they went him to seminary school.  The boy, however, longed to see the world, and so he decided to become a shepherd so that he could travel.  Although his father would have preferred that his son become a priest, he did give him three gold coins so that he could purchase his first flock and go out on his way.  He chose not to quench his son's choices by making him stay in the seminary, and he let the boy do as his his dictated.  This gave Santiago the strength to trust his intuition throughout the rest of the parable.

How does Santiago’s father react when Santiago wants to travel?

One of Coelho's basic points in the novel is that individuals sometimes cannot achieve their dreams because people in their lives have not been a source of encouragement, but rather a source of dissuasion in such pursuits.  Santiago's father would be one such source.  His reaction to his son's aspirations is to dissuade them.  He does not encourage his son and rejects the son's desires to dream and to travel.  Santiago's father suggests that those who pursue dreams are never satisfied.  Santiago's father wishes that his son pursue studies in becoming a priest, a profession that would give the family both social status and financial security.  Santiago's father has become blind to the ability to dream, something that animates his son.  In his embrace of the material, Santiago's father's reaction reflects the praising of what is as opposed to a condition of what can be.  Santiago's father does not stand in his son's way when he sets out to find his Personal Legend, but his reaction is not one of full throated support and encouragement.  This becomes one of the many obstacles and conditions that Santiago must fight through in order to follow a path in which his dreams are cradled and not crushed.