CS 3210 Design of Operating Systems
College of Computing, Georgia Tech

Lecture 2: Tuesday 18 January 2000

Program 1 / Board Checkout / Team Signups
A First Look at the Code (Maxwell Ch 2): printk() 

announcements

• roll
• photos
• handouts: p1
• board checkout / team signups

a first look at the code

• gcc-specific features (inline, expression blocks, optimization)
• gotos! (1 per 80 lines)

kernel coding style/idioms

• error variable idiom
• resource acquisition idiom (locking, unlocking)
• reduced use of #if and #ifdef
  • platform dependencies isolated in separate functions/macros
  • no compiler dependencies
  • some truly conditional code (SMP, etc.)

looking at source

• understand basic functionality (semantics)
• scan file for functions, global data
• read the comments :-)

kernel/printk()

• kernel printf
• log-levels 0-7 ("<6> Blah blah blah")
• maintains a 16k circular log_buf for recent stuff
• console(s) register drivers
  • printks possible before consoles registered!
• "flushes" on NEWLINE
• stdargs: va_start, va_end
• spinlock macros
• wait queue: wake_up_interruptible(&log_wait)
• optimizations?
• syslog, dmesg, syslogd, klogd, /proc/kmsg

wait queues

• queue of struct task_struct 
• #define wait_event(wq, condition)
• do { ... } while(0); idiom
• #define wait_even_interruptible(wq, condition)
• gcc expressional block feature ({...})

kernel modules

• dynamically linked/loaded kernel segments
• somewhat simplified interface to kernel proper
• may statically link modules
• + independent compilation
• can be dynamically removed
• kerneld ==> now kmod

configuring / building the kernel

• make config, menuconfig or xconfig
  • ==> result is .config (CONFIG_SMP=y etc.)
• don't alter configuration for now!
• make dep
• make zImage (zdisk, zlilo, bzimage, etc.)
• make clean (archclean, distclean, mrproper)
• see Linus' README for more details...

readings for next thursday (20 jan 2000)

• Maxwell Ch 4 Booting
• Beck Ch 3.2.3, Appendix D Booting
• Rubini Ch 16 Kernel Source Tour, Booting