Hello All ,
I'am facing a problem in the following
kernel module for a 2.4.16 kernel .
Here I'am not getting
the expected behaviour of "wait_event_interruptible".
Basically I'am trying to sleep on a
a condition (.i.e. a flag value is 0 ) in
"read "implementation . I have implemented
the unlocking mechanism in "write" implementation
(.ie. flag=1 ).
But the "read" implementation continues
to remain blocked , even if the condition
is satisfied when a "write" to the device
is done .
Kindly suggest me if I'am doing something
wrong . I have the code of the driver and
test routines below .
Thank you in Advance .
Regards
/***************************************************
Trying to write a Kernel module
which shows the usage of kernel waitqueue
The device acessed is having major=222 minor=0
This module is compiled as :
cc -c my.c -I/usr/src/linux/include
and inserted as module using :
insmod my.o my_major=222
****************************************************/
#ifndef __KERNEL__
# define __KERNEL__
#endif
#ifndef MODULE
# define MODULE
#endif
#include <linux/config.h>
#include <linux/module.h>
#include <linux/kernel.h> /* printk() */
#include <linux/slab.h> /* kmalloc() */
#include <linux/fs.h> /* everything... */
#include <linux/errno.h> /* error codes */
#include <linux/types.h> /* size_t */
#include <linux/wait.h>
#include <asm/page.h>
/* Device Major Number */
static int my_major = 0;
MODULE_PARM(my_major, "i");
MODULE_AUTHOR("learner");
int flag ;
/* Wait queue for this device */
wait_queue_head_t my_queue ;
/*
* Forwards for our methods.
*/
int my_open (struct inode *inode, struct file *filp);
ssize_t my_read(struct file *filp, char *buf, size_t
count, loff_t *f_pos);
ssize_t my_write(struct file *filp, const char *buf,
size_t count, loff_t *f_pos);
int my_release(struct inode *inode, struct file
*filp);
struct file_operations my_ops = {
read: my_read,
write: my_write,
open: my_open,
release: my_release,
};
/*
* Open the device; all we have to do here is to up
the usage count and
* set the right fops.
*/
int my_open(struct inode *inode, struct file *filp)
{
MOD_INC_USE_COUNT;
return 0;
}
/*
* Reading the Device
*/
ssize_t my_read(struct file *filp, char *buf, size_t
count,loff_t *f_pos)
{
printk( KERN_WARNING "read: Going to sleep on wait
queue" );
wait_event_interruptible( my_queue, flag );
printk( KERN_WARNING "read: Come out of sleep in
wait queue" );
printk( KERN_WARNING "read: Data Value %d \n",
flag );
return 0;
}
/*
* Writing the Device
*/
ssize_t my_write(struct file *filp, const char *buf,
size_t count,loff_t *f_pos)
{
printk( KERN_WARNING "write: Going to wake up
sleeping processes");
flag=1 ;
return 0;
}
/*
* Closing the Device
*/
int my_release(struct inode *inode, struct file *filp)
{
MOD_DEC_USE_COUNT;
return 0;
}
/*
* Module housekeeping.
*/
static int my_init(void)
{
int result;
SET_MODULE_OWNER(&my_ops);
result = register_chrdev(my_major, "my", &my_ops);
if (result < 0)
{
printk(KERN_WARNING "my: unable to get major
%d\n", my_major);
return result;
}
if (my_major == 0)
my_major = result;
init_waitqueue_head( &my_queue );
printk(KERN_WARNING "init: Initialised Wait queue
\n");
/* Initializing condition Flag to zero */
flag = 0 ;
return 0;
}
static void my_cleanup(void)
{
unregister_chrdev(my_major, "my");
}
module_init(my_init);
module_exit(my_cleanup);
*******************************************************
TEST ROUTINES
****************************************************
/* rtest : Program to read device
---------- it should block till the device writes
to device
*/
#include<fcntl.h>
main()
{
int fd ;
int data ;
fd = open("mydev",O_RDONLY );
read( fd, &data, sizeof(data) );
}
/* wtest : Program to write device
---------- it should unblocks device blocked on
read
*/
#include<fcntl.h>
main()
{
int fd ;
int data =0 ;
fd = open("mydev",O_WRONLY );
write( fd, &data, sizeof(data) );
}
********************************************
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