Socket Descriptors

• UNIX open yields a file descriptor:
  a small integer used to read/write a file

• UNIX keeps a file descriptor table for each process
  an array of pointers to data about open files

• A file descriptor is used to index the array

• Sockets are added to this abstraction

• The socket system call returns a socket descriptor

• Files and sockets are accessed using the same table

• The structure pointed to by a table entry has a field which tells whether it is a file or socket.