Understanding the Linux Kernel, 3rd Edition

Modern Age: the start_kernel( ) Function

The start_kernel( ) function completes the initialization of the Linux kernel. Nearly every kernel component is initialized by this function; we mention just a few of them:

• The scheduler is initialized by invoking the sched_init( ) function (see Chapter 7).

• The memory zones are initialized by invoking the build_all_zonelists( ) function (see the section "Memory Zones" in Chapter 8).

• The Buddy system allocators are initialized by invoking the page_alloc_init( ) and mem_init( ) functions (see the section "The Buddy System Algorithm" in Chapter 8).

• The final initialization of the IDT is performed by invoking trap_init( ) (see the section "Exception Handling" in Chapter 4) and init_IRQ( ) (see the section "IRQ data structures" in Chapter 4).

• The TASKLET_SOFTIRQ and HI_SOFTIRQ are initialized by invoking the softirq_init( ) function (see the section "Softirqs" in Chapter 4).

• The system date and time are initialized by the time_init( ) function (see the section "The Linux Timekeeping Architecture" in Chapter 6).

• The slab allocator is initialized by the kmem_cache_init( ) function (see the section "General and Specific Caches" in Chapter 8).

• The speed of the CPU clock is determined by invoking the calibrate_delay( ) function (see the section "Delay Functions" in Chapter 6).

• The kernel thread for process 1 is created by invoking the kernel_thread( ) function. In turn, this kernel thread creates the other kernel threads and executes the /sbin/init