Re: Char Driver Munmap

Jan Hudec wrote:

On Thu, Dec 14, 2006 at 04:25:14PM -0800, Manisha Maheshwari wrote:

I am writing a Char device driver.

I need to implement the munmap file operation for this driver.
Some how i couldn't find any infomation abt it in Linux device Driver book.

There is no such file_operation as munmap as of linux 2.6.18. Isn't that
the reason you can't find any info on it?
Can anybody provide the driver_munmap() code.
One way i know is -
In User space file - call munmap(mmaped_address, size);
Then switch to driver using - ioctl() and
In driver code, the memory allocated can be freed.
I dont think any specific driver_munmap() needed here as there is no file operation available.
If any other method , plz let us know.

Yes you are correct there is no file operation available for driver_munmap().

I wanted to do some state change when munmap is called for driver.

I found a way to do it :

In vm_area_struct stucture there is a field vm_ops which point to table of operation assciated with given memory.
This structure is intialized during driver_mmap().

Operation table describe open(),close etc method.
These method can be used to track map count and when map count drops to 0, driver_munmap() code can be called.

Here is code for implementing driver_munmap().

-----

static int count = 0;
void driver_munmap()
{
// i did state change here
}

void driver_vma_open(struct vm_area_struct *vma)
{
    count++;
    
}

void driver_vma_close(struct vm_area_struct *vma)
{
    count--;
 

  if ( count == 0)
  {
     // then it memory area is removed form address space of all process.
     // here you can call your driver_munmap(). 
     driver_munmap();

  }
}

------

For more explanation : Refer page 258 "Linux Kernel Development" by Robert love.

Correct me if I am wrong??

Thanks,
Manisha

Thanks in advance,
Manisha

--------------------------------------------------------------------------------
                  				- Jan Hudec `Bulb' 
<bulb@xxxxxx>

--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive:       
http://mail.nl.linux.org/kernelnewbies/
FAQ:           http://kernelnewbies.org/faq/