UDP socket not receiving full data.

Dear All, I have connected two machines A <---> B. B is sending 35 packets (packet size = 1042 bytes) of data to A over UDP socket. But, the application A is receiving only 12 packets. TCPDUMP on machine A is showing all the packets received on machine A. I suspect the erroneous buffer handling in TCP/IP stack. Can anyone please let me know the function which is responsible to transfer data from the kernel space to user space, the function which does copy_to_user() kind of stuff. Or any hint on the control path of data from the driver to the application will be helpful. Thanks, Prabhu