How open was it to allow foreigners to immigrate to be officials in the Tang Dynasty?

The policy of protection and attention in the Tang Dynasty was not as strict as it is now. Relatively speaking, it depends on the environment of the whole world at that time. At that time, the Tang Dynasty was very influential all over the world. Its relative openness is ok! Look at the murals and you will know how fat people were at that time and how good their living conditions were!