Hello Santosh and Anand,

Thanks for the reply and very good suggestions.

As Anand Moon suggested http://people.ee.ethz.ch/~arkeller/linux/multi/kernel_user_space_howto-3.html 
link in http://lists.kernelnewbies.org/pipermail/kernelnewbies/2012-November/006489.html previous thread, 


I read all the kernel to user space communication mechanism ( Except Upcall , ll read it). As of now for my application,


the signals passing from kernel to user space is enough. I was trying the sample code provided in  signals section of above link.

1. In the code he used find_task_by_pid_type, but find_task_by_pid_type not available in sched.h. So I have changed it to 


find_task_by_vpid(pid), is this right way ?

2. I tried to install the module but it is not finding the symbol, but the symbol is present in /proc/kallsyms.

Anything I am missing while compiling ? as I am getting warning.


Compile:

jeshwanth@jeshwanth:~/linux/kernel_user_space/code/signals$ make
make -C /lib/modules/3.0.0-26-generic-pae/build M=/home/jeshwanth/linux/kernel_user_space/code/signals modules
make[1]: Entering directory `/usr/src/linux-headers-3.0.0-26-generic-pae'
  Building modules, stage 2.
  MODPOST 1 modules
WARNING: "find_task_by_vpid" [/home/jeshwanth/linux/kernel_user_space/code/signals/signal_kernel.ko] undefined!
make[1]: Leaving directory `/usr/src/linux-headers-3.0.0-26-generic-pae'
[1]+  Done                    gedit signal_kernel.c

install Command:
root@jeshwanth:/home/jeshwanth/linux/kernel_user_space/code/signals# insmod signal_kernel.ko
insmod: error inserting 'signal_kernel.ko': -1 Unknown symbol in module

/proc/kallsyms:

00000000 T find_task_by_pid_ns
00000000 T find_task_by_vpid

dmesg:
[15012.556740] signal_kernel: Unknown symbol find_task_by_vpid (err 0)

Code:
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <asm/siginfo.h>    //siginfo
#include <linux/rcupdate.h>    //rcu_read_lock
#include <linux/sched.h>    //find_task_by_pid_type
#include <linux/debugfs.h>
#include <linux/uaccess.h>


#define SIG_TEST 44    // we choose 44 as our signal number (real-time signals are in the range of 33 to 64)

struct dentry *file;

static ssize_t write_pid(struct file *file, const char __user *buf,
                                size_t count, loff_t *ppos)
{
    char mybuf[10];
    int pid = 0;
    int ret;
    struct siginfo info;
    struct task_struct *t;
    /* read the value from user space */
    if(count > 10)
        return -EINVAL;
    copy_from_user(mybuf, buf, count);
    sscanf(mybuf, "%d", &pid);
    printk("pid = %d\n", pid);

    /* send the signal */
    memset(&info, 0, sizeof(struct siginfo));
    info.si_signo = SIG_TEST;
    info.si_code = SI_QUEUE;    // this is bit of a trickery: SI_QUEUE is normally used by sigqueue from user space,
                    // and kernel space should use SI_KERNEL. But if SI_KERNEL is used the real_time data
                    // is not delivered to the user space signal handler function.
    info.si_int = 1234;          //real time signals may have 32 bits of data.

    rcu_read_lock();
    //t = find_task_by_pid_type(PIDTYPE_PID, pid);  //find the task_struct associated with this pid
    t = find_task_by_vpid(pid);
    if(t == NULL){
        printk("no such pid\n");
        rcu_read_unlock();
        return -ENODEV;
    }
    rcu_read_unlock();
    ret = send_sig_info(SIG_TEST, &info, t);    //send the signal
    if (ret < 0) {
        printk("error sending signal\n");
        return ret;
    }
    return count;
}

static const struct file_operations my_fops = {
    .write = write_pid,
};

static int __init signalexample_module_init(void)
{
    /* we need to know the pid of the user space process
      * -> we use debugfs for this. As soon as a pid is written to
      * this file, a signal is sent to that pid
      */
    /* only root can write to this file (no read) */
    file = debugfs_create_file("signalconfpid", 0200, NULL, NULL, &my_fops);
    return 0;
}
static void __exit signalexample_module_exit(void)
{
    debugfs_remove(file);

}

module_init(signalexample_module_init);
module_exit(signalexample_module_exit);
MODULE_LICENSE("GPL");


On Thu, Nov 8, 2012 at 11:33 AM, SaNtosh kuLkarni <santosh.yesoptus@gmail.com> wrote:
I think you are looking for Upcall Functionality

upcall functionality allows a kernel module to invoke a function in user space. It is possible to start a program in user space, and give it some command line arguments, as well as setting environment variables.


**
int call_usermodehelper  (char * path, char ** argv, char ** envp, int wait);

Runs a user-space application. The application is started asynchronously if wait is not set, and runs as a child of keventd. (ie. it runs with full root capabilities).

Must be called from process context. Returns a negative error code if program was not execed successfully, or 0.

**man pages

Regards

Santosh




On Wed, Nov 7, 2012 at 8:30 PM, Bernd Petrovitsch <bernd@petrovitsch.priv.at> wrote:
Hi!

On Sam, 2012-11-03 at 19:14 +0530, Jeshwanth Kumar N K Jeshu wrote:
[...]
> Can I call userspace function from kernel module ? Actually I need to
> process some data in user space for every event occured in kernel module.

The usual way to implement this with a character device. The userspace
application opens the character device. It then read()s the events from
it, handles it and write()s results back (if needed).
The kernel part handles to IRQs, puts that into a buffer where it waits
for the read() from user space.

You can use netlink sockets for this which may save some code though or
implement a character device directly.

Kind regards,
        Bernd
--
Bernd Petrovitsch                  Email : bernd@petrovitsch.priv.at
                     LUGA : http://www.luga.at


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Santosh


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