question on char driver mmap

question on char driver mmap

[Chris Friesen]

I have a need for a device driver to map a page of memory between interrupt 
handlers and userspace.  It's been suggested that I use something like the 
following code (simplified):


unsigned long mypage;

int my_mmap(struct file *filp, struct vm_area_struct *vma)
{
	unsigned long offset = vma->vm_pgoff << PAGE_SHIFT;

	if (offset & ~PAGE_MASK)
		return -ENXIO;

	mypage =  __get_free_page(GFP_KERNEL);
	SetPageReserved(virt_to_page(mypage));
	remap_page_range(vma->vm_start, virt_to_phys((void *) mypage),
	                 PAGE_SIZE, vma->vm_page_prot);
	return 0;
}


This seems to work.  If I do this, however, do I need to hook into the munmap() 
file operations to handle unmapping, clearing the reserved bit, and freeing the 
page, or will the memory subsystem do it for me?

Thanks,

Chris