[SOLVED] copy_from/to_user how to use it simply to get pid into kernel space from userspace?

sindhu4sind · 05-22-2012, 04:22 AM

Hello everyone,

I am looking for providing userspace pid to kernel. And one of may be many ways is copy_from/to_user.
can anyone please help me to implement this? or can you give me some examples for this that i can overcome this problem:

kernel Code:

Code:

struct siginfo sinfo;
pid_t pid;
struct task_struct *task;
int init_module () {
memset(&sinfo, 0, sizeof(struct siginfo));
sinfo.si_signo = SIGIO;
sinfo.si_code = SI_USER;
pid = 5218; // Everytime a new PID 
task = pid_task(find_vpid(pid), PIDTYPE_PID); 
printk("%d .\n", task);
if(task == NULL) {
printk("Cannot find PID from user program\r\n");
return 0;
}
send_sig_info(SIGIO, &sinfo, task);
return 0;
}

Userspace Code:

Code:

void signal_handler (int signum){
if (signum == SIGIO) printf ("SIGIO\r\n"); return;
}
int main () {
int i=1 ;
signal(SIGIO, signal_handler);
printf("My PID is %d.\n",getpid());
while (i);
return 0;
}

How can i copy the userspace pid to kernel space by itself?

please help me out..

jhwilliams · 05-23-2012, 03:03 AM

The most common ways to get data from user space to kernel space are:

sysfs
procfs
chardev

There's a good discussion of these (and less popular methods), here:

http://people.ee.ethz.ch/~arkeller/l...ace_howto.html

Basically, you want to getpid(), and then write it to a file descriptor. That file descriptor will either be in /proc/something, or /sys/something, or /dev/something, depending on which of the above methods you choose.

Anyway, that's only a few lines of code. More of the work will be in the kernel module, where you implement one of the above interfaces.

sindhu4sind · 05-23-2012, 04:55 AM

Quote:

Originally Posted by jhwilliams

The most common ways to get data from user space to kernel space are:

sysfs
procfs
chardev

There's a good discussion of these (and less popular methods), here:

http://people.ee.ethz.ch/~arkeller/l...ace_howto.html

Basically, you want to getpid(), and then write it to a file descriptor. That file descriptor will either be in /proc/something, or /sys/something, or /dev/something, depending on which of the above methods you choose.

Anyway, that's only a few lines of code. More of the work will be in the kernel module, where you implement one of the above interfaces.

thank you so much jhwilliams.
I tried to work with ioctl..
but one thing strange is that, while i am making the device /dev/cdev_example using following command:

Quote:

# mknod /dev/cdev_example c 251 0
# chmod 666 /dev/cdev_example
# ls -l /dev/cdev_example
crw-rw-rw- 1 root root 251, 0 2012-05-23 02:37 /dev/cdev_example

It seems that device is created fine, but when i try to insert module it prints the message that:

Quote:

[540236.331549] cdev example: assigned major: 251
[540236.347809] create node with mknod /dev/cdev_example c 251 0

can you please tell me that why my created file/device is not working here?

i have also tried to check using:

Quote:

cat /dev/cdev_example

and
echo'd to device, but i am getting this message

Quote:

-su: /dev/cdev_example: No such device or address

sindhu4sind · 05-24-2012, 04:10 AM

Thank you so much for response jhwilliams...

I have got succeed in getting PID at kernel space:
Here I am posting code for helping the others:

Code:

#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h> //For file_operations struc
#include <linux/device.h> //For class create
#include <linux/slab.h> //For Kmalloc
#include <asm/uaccess.h> //copy_from_user and copy_to_user

pid_t id;
//int u_id;
static int major_no;
static struct class *my_class_0;

static int device_open(struct inode *inode, struct file *file){
	/*sucess*/
	return 0;
}

static int device_write(struct file *file, const char *gdata, size_t len, loff_t *off){
	get_user (id,(int *)gdata);
	if(id <0)
		printk("Cann't find PID from userspace its : %i", id);
	else
		printk("Hurrah! I got success.. here is it. %i", id);
	return len;
}

static int device_read(struct file *file, char *buf, size_t len, loff_t *off){
	
	return 0;
}

static int device_release(struct inode *inode, struct file *file){
	/*sucess*/
	return 0;
}

static struct file_operations fops = {
.open = device_open,
.write = device_write,
.read = device_read,
.release = device_release,
};

static int __init my_init(void){

major_no = register_chrdev(0, "my_dev", &fops);
my_class_0 = class_create(THIS_MODULE, "my_dev_0");
device_create(my_class_0, NULL, MKDEV(major_no, 0), NULL, "my_dev_0");
printk("\n Device Registered and Created \n");
return 0;
}

static void __exit my_exit(void){
printk("User PID : %d\n", id);
unregister_chrdev(major_no, "my_dev");

device_destroy(my_class_0, MKDEV(major_no,0));
class_unregister(my_class_0);
class_destroy(my_class_0);
printk("\n Device Un-Registered and Destroyed \n");
}

module_init(my_init);
module_exit(my_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR ("Raheel Ahmed Memon") ;
MODULE_DESCRIPTION ("Testing to get userspace PID into kernel space");

Makefile:

Code:

obj-m += k_module.o

all:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:	
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

Userspace Code:

Code:

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
//#include <sys/type.h>
#include <signal.h>

int main(){
int fd;
pid_t u_id;
u_id = getpid();

fd = open("/dev/my_dev_0",O_RDWR);
write(fd, &u_id, 4);
printf("\n PID sent to device successfully: %d \n", u_id);
close(fd);

while (1);
return 0;
}

Note: Remember one should run the Kernel Module before userspace application. so that when you will remove the module you can see the PID of userspace.

Thanks for response on my queries..

Raheel..