On Tue, 2005-12-20 at 14:32 +0200, John Que wrote:
[....]
> res of copy_to_user = 4
> Any idea?
Yes.
Where might the 4 come from?
And how do others use the return value?
[...]
> On 12/20/05, Bernd Petrovitsch <bernd@xxxxxxxxx> wrote:
> > On Tue, 2005-12-20 at 14:02 +0200, John Que wrote:
> > [...]
> > > I had written a very simple ioctl() method in a module;
> > > this ioctl calls copy_to_user();
> > >
> > > I am getting EFAULT when trying to call this ioctl from
> > > use space.
> > >
> > > Any idea what can be the reason ?
> >
> > Yes.
> >
> > > Here is the code:
> > >
> > > static unsigned long my_ioctl(struct inode* inode,
> > > struct file* file,
> > > unsigned int cmd,
> > > unsigned long data)
> > >
> > > {
> > > ...
> > > ...
> > > case MY_IOCTL:
> > > {
> > > unsigned int result = 99;
> > >
> > > if (copy_to_user((unsigned int *)data,
> > > &result,
> > > sizeof(unsigned int)))
> > > {
> > > printk("copy_to_user failed\n");
> > > return -EFAULT;
> > > }
> > >
> > > }
> >
> > What value is returned by copy_to_user()?
Bernd
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