Callback from kernel space to user space

I am implementing an RF chip driver that communicates over SPI.
I need to implement a user space call-back function to be invoked when an
interrupt is received.
I know how to register an interrupt hander in a kernel module but what is
the proper method of notifying the user space application?

Hello,

maybe you could take a look on how FUSE works (
http://fuse.sourceforge.net/ ) - it is a system which allows to create file
system drivers in user space.

Hi,

Use SIGNAL method in order to notify from the kernel module to user pace
program.

Before seding signal the kernel module need the process ID of the user
space program.

In the kernel module:

struct siginfo      sinfo;    /* signal information */
pid_t  pid;                   /* user program process id */
struct task_struct *task;


/* init */
memset(&sinfo, 0, sizeof(struct siginfo));  
sinfo.si_signo = SIGIO;    // Config the signals
sinfo.si_code  = SI_USER;  // Config SI_QUERE std or SI_KERNEL for RTC


pid = your_user_space_PID;

task = find_task_by_vpid (pid);           
if(task == NULL) {
   printk ("Cannot find pid from user program\r\n");
   return;
}

/* send SIGIO to the user program */
send_sig_info (SIGIO, &sinfo, task); /* Send signal to user program */ 


In user program :

void signal_handler (int signum) {
     if (signum == SIGIO) printf ("SIGIO\r\n");
     return;                  
}

struct sigaction action;
memset (&action, 0, sizeof (action)); /* clean variable */
action.sa_handler = signal_handler;   /* specify signal handler */
action.sa_flags = 0;                  /* operation flags setting */
sigaction (SIGIO, &action, NULL);     /* attach action with SIGIO */

Write fasync moduule in your driver and make your application ready for
SIGIO signal.Once any data comes to your ISR just send the SIGIO signal to
your application and from your application the registered signal handler
will do whatever the work you have assigned to this.

This was a good post from kamejoko80.