Re: [KJ] proper casting (if any) in copy_to_user() calls?

[Jaco Kroon <jaco@kroon.co.za>]

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Ahmed S. Darwish wrote:
> On Fri, Jan 05, 2007 at 08:54:28AM -0500, Robert P. J. Day wrote:
> 
>>you'll notice that numerous calls to copy_to_user() insist on casting
>>the pointer type of the first argument, despite the fact that that
>>first pointer is declared as being of type "void __user *" for the
>>routine itself, so it would seem no pointer is casting is required.
>>
>>  and yet, you can see that calls to copy_to_user() are casting the
>>first argument to (among other types) "char *" and "char __user *" and
>>"void *" and "void __user *" and "unsigned long *" and ... well, you
>>get the idea.  (the same can be said for the second argument to
>>copy_from_user().)
>>
>>  what is the proper rule for casting in this situation?  one would
>>think most of those casts are totally superfluous, no?
> 
> 
> I've written a patch to remove 30 unneeded copy_to_user casts in the infinband 
> subsystem (drivers/infiniband/core) and the result ?. I got 30 warning from 
> gcc while compiling :(.
> 
> The reason of the warnings was that the first argument of copy_to_user is
> unsigned long and not a pointer. so I get the infamous warning:
>  warning: passing argument 1 of ‘copy_to_user’ makes pointer from integer 
>  without a cast
> 
> So Janitors, I think it's better to remove the casts _only_ when the given 
> argument is a pointer and not an unsigned long (why do people use unsigned 
> long and not void* in the beginning anyway ?).

To prevent dereferencing an __user pointer?  But then imho that should
be standard right through the kernel and copy_(to,from)_user should take
unsigned long to begin with.

Jaco

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