Re: negative seek offsets in VFS

[Andi Kleen <ak@muc.de>]

> I don't think there is a "positive loff_t", so I guess the code would have 
> to be something like
> 
> 	/* Wraparound? */
> 	if ((u64)(pos + count) < count)
> 		goto Einval;

Sometimes I think we should have a nice inline asm macro for that
that checks carry. 

> 
> 	if ((loff_t) (pos + count) < 0)
> 		if (!(file->f_mode & FMODE_ANY_OFFSET))
> 			goto Einval;

Looks good. But how to handle the broken devices viro worries about? 
I would prefer not to open any new security holes, but it is a bit too
much code to audit all.  Flag would be possible, but ugly.

Any other choice?

-Andi