Hi, I am a newbie to linux and am trying to understand the linux input subsystem.
With the online help(which is prolifically available) I understood the basics to a certain extent. Although, there is one thing that I am not able to understand, here it goes :
Lets say there's a input device that is capable of generating an event with the help of its driver. Eg:
###############################################################################
/*
Driver to setup a Fake Input Device
by Sushiee
*/
#include <linux/input.h>
#include <linux/module.h>
#include <linux/init.h>
MODULE_LICENSE('GPL');
struct input_dev *dev_ip;
void dev_ip_timeout(unsigned long unused/*UNUSED*/)
{
/* letter S or s */
input_report_key(dev_ip, KEY_S, 1);
input_sync(dev_ip);
input_report_key(dev_ip, KEY_S, 0);
input_sync(dev_ip);
/* set timer for five second */
mod_timer(&(dev_ip->timer),jiffies+5*HZ );
}
static int __init ip_init(void)
{
/* initialization */
dev_ip = input_allocate_device();
//memset(&dev_ip, 0, sizeof(struct input_dev));
//init_input_dev(&dev_ip);
/* set up descriptive labels */
dev_ip->name = 'Con Device';
/* phys is unique on a running system */
dev_ip->phys = ';
dev_ip->id.bustype = BUS_HOST;
dev_ip->id.vendor = 0xDEAD;
dev_ip->id.product = 0xBEEF;
dev_ip->id.version = 0xFACE;
/* this device has one key S*/
set_bit(EV_KEY, dev_ip->evbit);
set_bit(KEY_S, dev_ip->keybit);
/* and finally register with the input core */
input_register_device(dev_ip);
/* set up a repeating timer */
init_timer(&dev_ip->timer);
dev_ip->timer.function = dev_ip_timeout;
dev_ip->timer.expires = 0;
add_timer(&dev_ip->timer);
return 0;
}
static void __exit ip_exit(void)
{
input_unregister_device(dev_ip);
}
module_init(ip_init);
module_exit(ip_exit);
###############################################################################
Its a driver for a virtual/fake device. One can complie it as a module and then install it by using : sudo insmod ./file_name.ko
Now, say this application is trying to access this device :
###############################################################################
#include <stdio.h>
#include <fcntl.h>
#include <linux/input.h>
#define EVENT_BUF_NUM 64
int main(int argc , char ** argv)
{
int fd = -1;
int i,version;
size_t read_bytes;
struct input_event event_buf[EVENT_BUF_NUM];
printf('Opening ..n');
fd = open('/dev/input/event6', O_RDONLY);
if(fd < 0) {
printf('nUnable to read from the devicen');
return(1);
}
printf('Reading ..n');
while(1) {
read_bytes = read(fd, event_buf, sizeof(struct input_event)*EVENT_BUF_NUM);
if( read_bytes < sizeof(struct input_event)) {
perror('bad read');
close(fd);
return(1);
}
for(i=0; i<(read_bytes/sizeof(struct input_event)); i++) {
switch(event_buf[i].type) {
case EV_SYN:
DPRINTF('---------------------------------------n');
break;
case EV_KEY:
switch(event_buf[i].value) {
case 0:
printf('Key Code: %d releasedn', event_buf[i].code);
break;
case 1:
printf('Key Code: %d pressedn', event_buf[i].code);
break;
case 2:
DPRINTF('Key pressed continuen', event_buf[i].code);
break;
default:
printf('UnKnown value: type %d, code %d, value %dn',
event_buf[i].type,
event_buf[i].code,
event_buf[i].value);
break;
}
break;
}
}
} /* end while */
close (fd);
}
###############################################################################
All, I want to know is where is the application getting the input_event structure from.
Who writes to this structure input_event?
does each device has a separate input_event structure? (I guess yes)
As,there is no input_event structure in any of these structues : struct device, struct input_dev, struct handle, struct handler. So, how is an input_event attached to the corresponding device.
Sorry for the long question.