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Advanced UNIX programming

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

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Advanced UNIX programming

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  1. 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

  2. Announcements • Reading assignment • Chapter 7 • Sections 7.1 – 7.6 and 7.9 – 7.11 • Chapter 8 • Midterm next Monday

  3. Week 9 Topics • Socket options • getsockopt, setsockopt • fcntl • ioctl • Introduction to UDP • TCP vs UDP • UDP interface

  4. Socket options • getsockopt, setsockopt • General socket options • IP options • TCP options • fcntl • ioctl

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. TCP options • level = IPPROTO_TCP, optname = • TCP_KEEPALIVE • Set the time • TCP_MAXRT • Maximum retransmission time • TCP_MAXSEG • Maximum segment size • See example1.c

  10. 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

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