Chapter 15

Team-Fly     TCP/IP Illustrated, Volume 2: The Implementation By Gary R. Wright, W. Richard Stevens Table of Contents Appendix A.  Solutions to Selected Exercises Chapter 15 15.1 The socket could be shared across a fork or passed to a process through a Unix domain socket ([Stevens 1990]). 15.2 The sa_len member of the structure is larger than the size of the buffer after accept returns. This is usually not a problem with the fixed-length Internet address, but it can be when using variable-length addresses supported by the OSI protocols, for example. 15.4 The call to soqremque is only made when so_qlen is not equal to 0. If soqremque returns a null pointer there must be an error in the socket queueing code so the kernel panics. 15.5 The copy is made so that bzero can clear the structure while it is locked and so that dom_dispose and sbrelease can be called after splx. This minimizes the amount of time the CPU is kept at splimp and therefore the amount of time that network interrupts are blocked. 15.6 The sbspace macro will return 0. As a result, the sbappendaddr and sbappendcontrol functions (used by UDP) will refuse to queue additional packets. TCP uses sbappend, which assumes that the caller has checked for space first. TCP calls sbappend even when sbspace returns 0. The data placed in the receive queue is not available to a process because the SS_CANTRCVMORE flag prevents the read system calls from returning any data. Team-Fly     Top