keyboard stroke consecutive key are not capturing - linux-kernel

Question

This is an assignment and I have written a Linux driver where we have to capture the key stroke.
We've divided the task in top and bottom halves (work queue). I'm able to log properly the normal key stroke like a,b,1,2 etc. but when we press long any character it is logging 7 extra letter.
For example when I consecutive press (a) like aaa my log file show aaaaaaaaaa it echos 7 extra a.
Can anybody tell what might be the root cause?
EDIT #1
WORK QUEUE CODE
// WORK QUEUE
static void got_char(my_work_cls *work_str)
{
char fileinfo_buff[200], path[120];
strcpy(fileinfo_buff,"");
printk(KERN_INFO "Scan Code %d %x %s.\n",
work_str->scancode,
work_str->scancode & 0x7F,
work_str->scancode & 0x80 ? "Released" : "Pressed");
if(!(work_str->scancode & 0x80))
{
printk(KERN_INFO "Scancode BFSHFT=%s ",key[work_str->scancode]);
if(work_str->scancode==42 || work_str->scancode==54 || shpress==1)
{
if(shpress==1 && ( work_str->scancode!=42 || work_str->scancode!=54) )
{
if(((work_str->scancode)+70)<=len)
{
printk(KERN_INFO "Scancode SHFT=%s",key[(work_str->scancode)+70]);
strcat(fileinfo_buff,key[(work_str->scancode)+70]);
}
}
shpress=1;
}
else
{
if(work_str->scancode==28)
{
printk(KERN_INFO "Scancode En=%s",key[work_str->scancode]);
strcat(fileinfo_buff,"\n");
}
else
{
printk(KERN_INFO "Scancode S=%s",key[work_str->scancode]);
strcat(fileinfo_buff,key[work_str->scancode]);
}
}
}
else
{
if(((work_str->scancode)-128)==42 || ((work_str->scancode)-128)==54)
{
printk(KERN_INFO "Scancode RL=%s",key[((work_str->scancode)-128)]);
shpress=0;
}
}
}
interrupt handler code
// interrupt handler
irqreturn_t irq_handler(int irq, void *dev_id, struct pt_regs *regs)
{
/*
* This variables are static because they need to be
* accessible (through pointers) to the bottom half routine.
*/
static int initialised = 0;
static unsigned char scancode;
static struct work_struct task;
unsigned char status;
/*
* Read keyboard status
*/
status = inb(0x64);
scancode = inb(0x60);
printk(KERN_INFO "In F Scancode=%d",scancode);
work_str = (my_work_cls *)kmalloc(sizeof(my_work_cls), GFP_KERNEL);
if (initialised == 0)
{
printk(KERN_INFO "If Scancode=%d",scancode);
if (work_str)
{
INIT_WORK((struct work_struct *)work_str, got_char);
work_str->scancode = scancode;
initialised = 1;
}
}
else
{
PREPARE_WORK((struct work_struct *)work_str, got_char);
work_str->scancode = scancode;
}
queue_work(my_workqueue, (struct work_struct *)work_str);
return IRQ_HANDLED;
}

Answer 1

Each a logged in the kernel-driver signifies a keyevent received from the hardware.
Hardware -> Kernel-Driver -> Display server -> Window manager -> App -> Screen
On a GUI system, the userspace display-server, window-manager and the application are free to choose to ignore the keyevent. This is usually done to eliminate an accidental long keypress from being recognised as multiple keypresses.
On X, the option AutoRepeat <delay> <rate> sets the auto-repeat behaviour for the keyboard.
Delay is the time in milliseconds before a key starts repeating.
Rate is the number of times a key repeats per second.
For example Autorepeat 500 30 configures X to :
- Ignore the keyevent(of the same key) from the hardware for 500ms.
- After 500ms, only one keyevent(of the same key) is accepted every 30ms.
Also any keyevent for a different hardware key restarts this entire procedure to calculate auto-repeat.
NOTE: Such auto-repeat delay and rate limiting is often also implemented in applications themselves. So even in absence of X, it is common to observe a discrepancy between the number of keys reported by the kernel keyboard driver and the text displayed on screen within an application.