Tasklet-2 using tasklet_init

In the previous post we saw the basics of a tasklet, now let us look at an example module that creates a tasklet.

We will use the function "tasklet_init" to create the tasklet in this example.

In this module we will create a read proc entry called "initask". On reading this proc entry a tasklet will get initialized and scheduled.

The function executed on reading the proc etnry will be :

int initask(char *buf, char **start, off_t offset,int len, int *eof, void *arg) { printk(KERN_INFO " In proc initask"); task = kmalloc(sizeof(struct tasklet_struct),GFP_KERNEL); tasklet_init(task,task_fn,0); tasklet_schedule(task); *eof =1; return 0; }

Working :

task = kmalloc(sizeof(struct tasklet_struct),GFP_KERNEL);

This line allocates memory for a new tasklet and returns a pointer to the structure.

tasklet_init(task,task_fn,0);

This initates the tasklet "task" . The function that will be executed as a part of the tasklet is "task_fn" which has to be implemented in the module.

In our "task_fn" we will just print the state and value of count of the tasklet. In real tasklets, it is here that the main work happens.

task_fn:

void task_fn(unsigned long arg) { printk(KERN_INFO "In tasklet function"); printk(KERN_INFO "\n The state is %d",task->state); printk(KERN_INFO "\n The count is %d",task->count); }

The init and exit functions are going to be pretty simple as we have nothing much to do in them.

init and exit functions: int st_init(void) { create_proc_read_entry("initask",0,NULL,initask,NULL); return 0; } void st_exit(void) { remove_proc_entry("initask",NULL); }

Thus the full code of the module with the required header files will look as follows tasklet_init.c #include<linux/kernel.h> #include<linux/module.h> #include<linux/init.h> #include<linux/proc_fs.h> // Required for proc entry creation #include<linux/sched.h> #include<linux/interrupt.h> // Required for tasklet_struct struct tasklet_struct *task; void task_fn(unsigned long arg) { printk(KERN_INFO "In tasklet function"); printk(KERN_INFO "\n The state is %d",task->state); printk(KERN_INFO "\n The count is %d",task->count); } int initask(char *buf, char **start, off_t offset, int len, int *eof, void *arg) { printk(KERN_INFO " In proc initask"); task = kmalloc(sizeof(struct tasklet_struct),GFP_KERNEL); tasklet_init(task,task_fn,0); tasklet_schedule(task); *eof =1; return 0; } int st_init(void) { create_proc_read_entry("initask",0,NULL,initask,NULL); return 0; } void st_exit(void) { remove_proc_entry("initask",NULL); } module_init(st_init); module_exit(st_exit);

Save the code as tasklet_init.c

The Makefile required for this is

ifneq ($(KERNELRELEASE),) obj-m := tasklet_init.o else KERNELDIR ?= /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) default: $(MAKE) -C $(KERNELDIR) M=$(PWD) modules clean: $(MAKE) -C $(KERNELDIR) M=$(PWD) clean endif

To see the output run the following commands

$ make

If there are no errors then continue.

$ sudo insmod tasklet_init.ko $ cat /proc/initask $ dmesg | tail -5

Ouptut: In proc initask In tasklet function The state is 2 The count is 0

You shoud see the above lines being printed in the logs.

We scheduled the tasklet when proc entry was read, our processor was not heavily loaded hence the tasklet got scheduled immediately and thus the "task_fn" got executed.

The state "2" signifies the tasklet is running and the count being 0 signifies tasklet is enabled.