Advanced UNIX programming
Fall 2002
Instructor: Ashok Srinivasan
Lecture 23
Acknowledgements: The syllabus and power point presentations are modified versions of those by
T. Baker and X. Yuan
Announcements
• Reading assignment
– Chapter 7
• Sections 7.1 – 7.6 and 7.9 – 7.11
– Chapter 8
– Midterm next Monday
Week 9 Topics
• Socket options
– getsockopt, setsockopt
– fcntl
– ioctl
• Introduction to UDP
– TCP vs UDP
– UDP interface
Socket options
• getsockopt, setsockopt
– General socket options
– IP options
– TCP options
• fcntl
• ioctl
getsockopt, setsockopt
– #include <sys/socket.h>
int getsockopt (int sockfd, int level, int optname,
void *optval, socklen_t *optlen);
int setsockopt(int sockfd, int level, int optname,
const void *optval, socklen_t optlen);
• The level includes general socket options
(SOL_SOCKET) and protocol-specific options
(for IP, TCP, etc).
• Option value can be of different types: pointers
to int, in_addr, timeval, etc
General socket options
• level = SOL_SOCKET, optnames =
– SO_BROADCAST
• Permit sending broadcast datagram
– SO_KEEPALIVE
• For TCP only, automatically send a keepalive
message when inactive for 2 hours (can be
modified)
– SO_LINGER
• for TCP only, determines behavior on close
– SO_RCVBUF, SO_SNDBUF
• Send and receive buffer size
General socket options (continued)
• level = SOL_SOCKET, optnames =
– SO_RCVLOWAT, SO_SENDLOWAT
• low watermark – affects the select system call
– SO_RCVTIMEO, SO_SNDTIMEO
• Inherent timeout time (disabled by default)
– SO_TYPE
• Socket type: SOCK_STREAM and
SOCK_DGRAM
– Etc.
IP options
• Allows packets sent through a socket to have
certain behavior
– For example, source routing
– level = IPPROTO_IP
• optname (manipulating IP header fields)
– IP_OPTIONS
– IP_RECVDSTADDR
– IP_RECVIF
– IP_TOS
– IP_TTL
– Etc.
TCP options
• level = IPPROTO_TCP, optname =
– TCP_KEEPALIVE
• Set the time
– TCP_MAXRT
• Maximum retransmission time
– TCP_MAXSEG
• Maximum segment size
• See example1.c
fcntl and ioctl
• fcntl
– File control on open files
• Set file descriptor flags (FD_CLOEXEC)
• Non-blocking mode, etc.
• ioctl
– Some I/O control operations