Some kernel facilities—those associated with filesystems, memory
management, and networking—live in their own source trees. The
kernel directory of the source tree includes all
other basic facilities.
The most important such facility is scheduling. Thus,
sched.c, together with
<linux/sched.h>, can be considered the most
important source file in the Linux kernel. In addition to the
scheduler proper, implemented by schedule, the
file defines the system calls that control process priorities and all
the mechanisms for sleeping and waking.
The fork and exit system calls are implemented by two files that are named after them. They are comprehensive and well-structured files that deal with everything related to process creation and destruction.
The delivery of kernel messages is implemented in
printk.c, which is also concerned with console
management. Console code is not trivial, since the concept of
“console” is pretty abstract nowadays and includes the text screen
(either native or based on the frame buffer), the serial port, and
even the printer port.
Other facilities that are implemented in this directory are time
handling (time.c), kernel timers
(timer.c), signal delivery and handling
(signal.c), module management and related system
calls (module.c), the
kmod thread (kmod.c),
systemwide power management (pm.c), tasklets
(softirq.c), and the panic function
(panic.c).
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