On Wed, Mar 27, 2002 at 02:40:17PM +0530, shahnavaz wrote:
> I have written a small code to understand copy_to/from_user.
>
> I know there are lots of mistake in the code.Can someone correct
> me..*Please*.I have searched a lot in this context but in vain.I cannot find
> any suitable example in "Linux Device Driver "Book in this context.
Uhm, there are *plenty* of examples in that book. All character driver
examples use copy_to_user(). If you think that's not enough, there is
about 50MB worth of driver code in the drivers directory in each
kernel, so I can't imagine there isn't a suitable example.
> #include ...
> int test_major=0,major;
> char *data="copy_to_user",*buf;
>
> struct file_operations test_fops={
> ...
> };
>
> int init_module()
> {
> int count;
> major=register_chrdev(test_major,"Test",&test_fops);
> if(major < 0)
> {
> printk(KERN_WARNING"cant get major %d\n",test_major);
> return -1;
> }
> else
> printk(KERN_WARNING"major number is %d\n",major);
> count=copy_to_user(buf,data,13);
This will fail. copy_to_user() needs a _userland_ buffer, and you just
provided it with a NULL pointer. copy_to_user() should be used in the
read() method of your driver, not in init_module(). For a simple
example, look at the function wdt_read() in drivers/char/wdt.c .
Erik
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J.A.K. (Erik) Mouw, Information and Communication Theory Group, Faculty
of Information Technology and Systems, Delft University of Technology,
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