single entry or double entry visa

HEllo..i am from India and plan to visit China next month. I plan to land in HK and take a train to Guangzhou . and I want to spend 3 4 days there...Again i want to fly back from HK. So do i need a single entry or a double entry type? Also if i take a tourist L type entry permit does it anyway prohibit me to meet vendors or visit some manufacturing , trading centres in China?

Kindly help.
regards
Rahul