Hello Jan ,
Thanks for the reply .
I understood that we need to do both ,i.e.
satisfy condition & also wakeup , to come out
of "wait_event_interruptible()".
But this can be achieved using
"sleep_on_interruptible" and doing a
"wakeup_interruptible" after checking
the condition .
Does "wait_event_interruptible"
need to be used in any specific
scenario or in any particular
situation ?
Kindly explain ,where specifically
do we need to use each of these variants
of wait-sleeps ?
Thanks in advance .
Regards !
--- Jan Hudec <bulb@ucw.cz> wrote: > On Mon, Feb 24,
2003 at 11:45:55AM +0000,
> Anticipating a Reply wrote:
> > 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".
>
> You are geting the expected behaviour. You are not
> waking up the queue!
>
> The wait_event_interruptible goes to sleep while the
> condition is false.
> When it goes to sleep, you need to wake it up. You
> need to:
> flag = 1;
> wake_up(my_queue);
>
> Note: You should use atomic operations for the flag
> ;-).
>
> > 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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> > --
> > Kernelnewbies: Help each other learn about the
> Linux kernel.
> > Archive:
> http://mail.nl.linux.org/kernelnewbies/
> > FAQ: http://kernelnewbies.org/faq/
> >
>
-------------------------------------------------------------------------------
> Jan 'Bulb' Hudec <bulb@ucw.cz>
> --
> Kernelnewbies: Help each other learn about the Linux
> kernel.
> Archive:
> http://mail.nl.linux.org/kernelnewbies/
> FAQ: http://kernelnewbies.org/faq/
>
________________________________________________________________________
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--
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Archive: http://mail.nl.linux.org/kernelnewbies/
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