mmap sync issue

[Gil Weber <gilw@cse-semaphore.com>]

Hello,
I am experiencing an issue with my device driver. I am using mmap and ioctl to share information with my user space application.
The thing is that the shared memory does not seems to be synced. Do check this, I have done a simple test:

int fd = open("/dev/test", O_RDWR | O_SYNC);
int * addr = mmap(0, 4, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
	
for (i=0 ; i<100 ; i++ )
{
	*addr = i;
	ioctl(fd, 0, 0);
}


In my device driver, the only thing I do in ioctl is to display the content of the shared memory, and here is the result:

[ 5158.967000] Value : 0
[ 5158.967000] Value : 1
[ 5158.967000] Value : 1
[ 5158.967000] Value : 1
[ 5158.967000] Value : 1
[ 5158.967000] Value : 1
[ 5158.967000] Value : 1
[ 5158.967000] Value : 1
[ 5158.967000] Value : 1
[ 5158.967000] Value : 1
[ 5158.967000] Value : 1
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
[ 5158.968000] Value : 11
...


So, clearly, memory is not synced...
Here is the code in my device driver:

static int test_open(struct inode *inode, struct file *filp)
{
	return 0;
}

static int test_release(struct inode *inode, struct file *filp)
{
	return 0;
}

static int test_mmap(struct file *filp, struct vm_area_struct *vma)
{
	int ret;
	unsigned long start = vma->vm_start;
	unsigned long pfn;

	pfn = vmalloc_to_pfn(vmalloc_area);
	if ((ret = remap_pfn_range(vma, start, pfn, PAGE_SIZE, PAGE_SHARED)) < 0) {
		return ret;
	}
	
	return 0;
}

static long test_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	printk (KERN_INFO "Value : %d\n", vmalloc_area[0]);
	return 0;
}

static struct file_operations test_fops = {
	.open = test_open,
	.release = test_release,
	.mmap = test_mmap,
	.unlocked_ioctl = test_ioctl,
	.owner = THIS_MODULE,
};

This is done on an arm architecture (AT91 SAM9X5) with a kernel 3.5.
I have done the test, with the same code, on a powerpc target, with a kernel 2.6.27, and it seems to work (but maybe by chance?)
Am I missing something?
Maybe I need to implement the sync function in file operations, but in that case, how can I know that all mapped memory is synced?

Thanks in advance,
Gil Weber

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