3.1 Describe three types of system activity.
3.2 When can a routine executing in the top half of the kernel be preempted? When can it be interrupted?
3.3 Why are routines executing in the bottom half of the kernel precluded from using information located in the current user process?
3.4 Why does the system defer as much work as possible from high-priority interrupts to lower-priority software-interrupt processes?
3.5 What determines the shortest (nonzero) time period that a user process can request when setting a timer?
3.6 How does the kernel determine the system call for which it has been invoked?
3.7 How are initialized data represented in an executable file? How are uninitialized data represented in an executable file? Why are the representations different?
3.8 Describe how the "#!" mechanism can be used to make programs that require emulation appear as though they were normal executables.
3.9 Is it possible for a file to have permissions set such that its owner cannot read it, even though a group can? Is this situation possible if the owner is a member of the group that can read the file? Explain your answers.
*3.10 Describe the security implications of not zero filling the stack region at program startup.
*3.11 Why is the conversion from UTC to local time done by user processes rather than in the kernel?
*3.12 What is the advantage of having the kernel rather than an application restart an interrupted system call?
*3.13 Describe a scenario in which the timer-wheel algorithm used for the callout queue does not work well. Suggest an alternative data structure that runs more quickly than does the timer-wheel algorithm for your scenario.
*3.14 The SIGPROF profiling timer was originally intended to replace the profil system call to collect a statistical sampling of a program's program counter. Give two reasons why the profil facility had to be retained.
**3.15 What weakness in the process-accounting mechanism makes the latter unsuitable for use in a commercial environment?
