Go from a file number to its socket slot
struct socket * sockfd_lookup(int fd, int * err);
fd
file handle
err
pointer to an error code return
The file handle passed in is locked and the socket it is bound too is returned. If an error occurs the err pointer is overwritten with a negative errno code and NULL is returned. The function checks for both invalid handles and passing a handle which is not a socket.
On a success the socket object pointer is returned.