Re: copy_to_user problem

[Kanoj Sarcar <kanojsarcar@yahoo.com>]

Can you try copy_to_user(), and not __copy_to_user().

Kanoj

--- PRASENJIT CHAKRABORTY <pras_chakra@yahoo.com>
wrote:
> Hello All,
> 
>    I posted this problem some days back but still
> have
> not received any solution.
> 
> So sorry for the resend again.
> 
> I am developing a driver. Though the driver is
> functioning well but I am stuck up at the point of
> transferring something from kernel to user space.
> 
> I am using __copy_to_user() and before calling this
> I
> am checking the validity of user address with
> verify_area().
> 
> Now the problem is that __copy_to_user() sometimes
> return value > 0 which indicates a failure. This
> happens everytime the user address is not currently
> present in the Physical Page i.e the when
> __copy_to_user tries to copy to a page which is not
> currently paged in then it fails.
> 
> Moreover if I access the user buffer from my user
> program before passing it to the kernel for transfer
> then __copy_to_user performs it happily or if I lock
> that page through mlock() system call. I read the
> documentation but nowhere I found that I need to do
> something before __copy_to_user().
> 
> The problem for the time being has been workarounded
> by putting __verify_write() before __copy_to_user.
> 
> So I would like to know what is wrong with my
> approach
> or is it due to some other issue which is unknown to
> me (e.g corruption etc).
> 
> I shall be grateful to you all if you kindly help me
> out of this.
> 
> Thanks n Regards,
> 
> Prasenjit
> 
> 
> 
> 
> 
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