processes

Code for managing processes. More...

Files
file	fork.c
	Implementation of fork-related functions.
file	process.c
	Implementation of functions for creating and killing processes.
file	scheduler.c
	Implementation of scheduler functions.
file	scheduler.h
	Definition of armv6 scheduler helper functions.
file	scheduler.h
	Definition of armv8-a scheduler helper functions.
file	fork.h
	Definition of fork-related functions.
file	process.h
	Definition of functions for creating and killing processes.
file	scheduler.h
	Definition of scheduler structs and functions.

Data Structures
struct	cpu_context
struct	task_struct

Macros
#define	THREAD_CPU_CONTEXT   0
#define	THREAD_CPU_CONTEXT   0
#define	TASK_RUNNING   0
#define	NR_TASKS   64
#define	FIRST_TASK   task[0]
#define	LAST_TASK   task[NR_TASKS-1]
#define	THREAD_SIZE   4096
#define	INIT_TASK   { /* cpu_context */ {0,0,0,0,0,0,0,0,0,0,0,0,0}, /* state etc */ 0,0,1,0 }

Functions
int	copy_process (uint64_t fn, uint64_t arg)
void	create_processes (size_t proc_num)
void	kill_processes ()
void	ret_from_fork ()
void	cpu_switch_to (task_struct *prev, task_struct *next)
void	preempt_disable ()
void	preempt_enable ()
void	schedule_tail ()
void	switch_to (task_struct *next)
void	schedule ()
void	timer_tick ()

Variables
task_struct *	task [NR_TASKS]
task_struct *	current
int	nr_tasks

Detailed Description

Code for managing processes.

Macro Definition Documentation

FIRST_TASK

#define FIRST_TASK   task[0]

Define the first task.

See also

task

INIT_TASK

#define INIT_TASK   { /* cpu_context */ {0,0,0,0,0,0,0,0,0,0,0,0,0}, /* state etc */ 0,0,1,0 }

Defines the init task's task_struct ( kernel_main()) that is run on kernel startup.

Fields:

• cpu_context: All registers initialized to 0.
• state = 0 ( TASK_RUNNING)
• counter = 0
• priority = 1
• preempt_count = 0 (can be rescheduled)

See also

task_struct, cpu_context, TASK_RUNNING

LAST_TASK

#define LAST_TASK   task[NR_TASKS-1]

Define the last task.

See also

task

NR_TASKS

#define NR_TASKS   64

Maximum number of concurrent tasks

TASK_RUNNING

#define TASK_RUNNING   0

Task States

THREAD_CPU_CONTEXT [1/2]

#define THREAD_CPU_CONTEXT   0

Offset of cpu_context in task_struct.

THREAD_CPU_CONTEXT [2/2]

#define THREAD_CPU_CONTEXT   0

Offset of cpu_context in task_struct.

THREAD_SIZE

#define THREAD_SIZE   4096

Defines size of each process.

Equal to the Page size ( PAGE_SIZE).

Function Documentation

copy_process()

int copy_process	(	uint64_t	fn,
		uint64_t	arg
	)

Function for creating a new process.

Parameters

fn	A function to execute in a new thread.
arg	An argument that need to be passed to this function.

Returns

• On success: 0
• On failure: 1

Allocates a new task_struct and makes it available for the scheduler.

See also

task_struct, get_free_page()

cpu_switch_to()

void cpu_switch_to	(	task_struct *	prev,
		task_struct *	next
	)

Performs the context switch, by changing the registers.

Parameters

prev	Pointer to the task_struct of the task we are switching (Starting address of memory page of the new task).
next	Pointer to the next task_struct.

See also

scheduler.S

create_processes()

void create_processes

(

size_t

proc_num

)

Creates processes using copy_process().

Parameters

proc_num

Number of processes to fork.

Maximum number of processes that can be created is NR_TASKS.

See also

copy_process(), NR_TASKS, task_struct

kill_processes()

void kill_processes

(

)

Kills all running processes (except init_task).

Do for each process:

• Get starting address of process.
• Check that it is not the current process (init_task).
• Free page.
• Decrease number of processes (Decrease nr_tasks).
• Remove task_struct from task array (Set task[pid] = 0).

See also

free_page(), preempt_disable(), task_struct

preempt_disable()

void preempt_disable

(

)

Disables preemption for current running process.

preempt_enable()

void preempt_enable

(

)

Enables preemption for current running process.

ret_from_fork()

void ret_from_fork

(

)

Starting point for each new task.

PC register (cpu_context.pc) of each new task points here.

See also

scheduler.S

schedule()

void schedule

(

)

Main scheduler function.

Wrapper for core scheduler function _schedule(). Checks whether there is a new task, that needs to preempt the current one.
Gets called:

• Explicitly by another task.
• From timer interrupt handler.

See also

switch_to(), task, preempt_disable(), preempt_enable()

schedule_tail()

void schedule_tail

(

)

Tail function that enables preemption for current process.

It is the last function a new task calls, after its initialization, in order for it to be rescheduled.

See also

preempt_enable()

switch_to()

void switch_to

(

task_struct *

next

)

Function that switches from current to the next task.

Parameters

next	A task_struct pointer, that points to the next task.

Calls cpu_next_to, in order to perform the necessary context switch.

See also

task_struct

timer_tick()

void timer_tick

(

)

Calls _schedule() after a time interval.

Gets called from System Timer interrupt handler.

See also

handle_timer_3_irq(), _schedule()

Variable Documentation

current

task_struct* current

Pointer that points to the currently executing task.

Holds a pointer to the init_task.

nr_tasks

int nr_tasks

Number of currently running tasks.

Number of currently running tasks = 1 (init_task)

task

task_struct* task[NR_TASKS]

Array that holds all the tasks.

Appends a pointer to the init_task.