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title:Create threads
keywords:kernel,linux,threads
# Create threads
## Starting point
__Makefile__
```Makefile
obj-m += create_thread.o
KDIR ?= /lib/modules/$(shell uname -r)/build
all:
make -C $(KDIR) M=$(PWD) modules
clean:
make -C $(KDIR) M=$(PWD) clean
```
__create_thread.c__
```c
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h>
int create_thread_init( void )
{
printk(KERN_DEBUG "Hello Thread!\n");
return 0;
}
void create_thread_exit( void )
{
printk(KERN_DEBUG "Exit Thread!\n");
}
module_init( create_thread_init );
module_exit( create_thread_exit );
MODULE_LICENSE("GPL");
```
## Create empty thread
Lets create kernel thread that will start and exit straight away
```c
#include <linux/delay.h>
static struct task_struct *task;
static int run_task(void *data) {
int i=0;
while(!kthread_should_stop())
{
pr_info("run task%d\n", i++);
msleep(1000);
}
return 0;
}
int create_thread_init( void ) {
...
task = kthread_create(run_task, NULL, "special task");
if(task)
{
wake_up_process(task);
} else {
printk(KERN_ERR "Cannot create kthread\n");
}
...
}
```
## Kernel threads states
State of kernel thread - include/linux/sched.h
```c
/* Used in tsk->state: */
#define TASK_RUNNING 0x00000000
#define TASK_INTERRUPTIBLE 0x00000001
#define TASK_UNINTERRUPTIBLE 0x00000002
#define __TASK_STOPPED 0x00000004
#define __TASK_TRACED 0x00000008
/* Used in tsk->exit_state: */
#define EXIT_DEAD 0x00000010
#define EXIT_ZOMBIE 0x00000020
#define EXIT_TRACE (EXIT_ZOMBIE | EXIT_DEAD)
/* Used in tsk->state again: */
#define TASK_PARKED 0x00000040
#define TASK_DEAD 0x00000080
#define TASK_WAKEKILL 0x00000100
#define TASK_WAKING 0x00000200
#define TASK_NOLOAD 0x00000400
#define TASK_NEW 0x00000800
#define TASK_RTLOCK_WAIT 0x00001000
#define TASK_FREEZABLE 0x00002000
#define __TASK_FREEZABLE_UNSAFE (0x00004000 * IS_ENABLED(CONFIG_LOCKDEP))
#define TASK_FROZEN 0x00008000
#define TASK_STATE_MAX 0x00010000
#define TASK_ANY (TASK_STATE_MAX-1)
```
## List of kernel thread functions used
| Function name | Note |
|---|---|
| | |
| wake_up_proces | |
| kthread_create | |
## Final result
__create_thread.c__
```c
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/kthread.h>
#include <linux/err.h>
#include <linux/uaccess.h>
#include <linux/cdev.h>
#include <linux/delay.h>
static struct task_struct *task;
static int run_task(void *data) {
int i=0;
while(!kthread_should_stop())
{
pr_info("run task %d\n", i++);
msleep(1000);
}
return 0;
}
int create_thread_init( void )
{
printk(KERN_DEBUG "Hello Thread!\n");
task = kthread_create(run_task, NULL, "special task");
if(task)
{
wake_up_process(task);
} else {
printk(KERN_ERR "Cannot create kthread\n");
}
return 0;
}
void create_thread_exit( void )
{
printk(KERN_DEBUG "Exit Thread!\n");
}
module_init( create_thread_init );
module_exit( create_thread_exit );
MODULE_LICENSE("GPL");
```
## Links
https://www.linuxtoday.com/blog/kernel-threads/
http://www.embeddedlinux.org.cn/EssentialLinuxDeviceDrivers/final/ch03lev1sec1.html
https://embetronicx.com/tutorials/linux/device-drivers/linux-device-drivers-tutorial-kernel-thread
https://elixir.bootlin.com/linux/v6.1.21/source/include/linux/sched.h
https://elixir.bootlin.com/linux/v6.1.21/source/kernel/sysctl.c
https://girishjoshi.io/post/creating-linux-kernel-threads/
https://tuxthink.blogspot.com/2011/02/kernel-thread-creation-1.html
https://elixir.bootlin.com/linux/v6.1.21/source/include/linux/kthread.h#L27
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