Re: [PATCH] new ioctl type checking causes gcc warning

["Kevin P. Fleming" <kpfleming@cox.net>]

Arnd Bergmann wrote:

> This doesn't work, because size_t is a typedef, not a macro.

Yeah, I should have thought of that. Sorry.

> The type checking this in user space is not necessary, because 
> the point of the check is only to keep people from adding *new*
> invalid ioctl numbers and doing the check for the kernel does that.
> However, the old numbers need to be kept for a long time and there
> is no point in breaking user applications that use established
> interfaces.

Hmm, obviously I misunderstood how this worked. Does that mean that 
these two lines:

#define BLKGETSIZE64	_IOR(0x12,114,sizeof(__uint64_t))
#define BLKGETSIZE64	_IOR(0x12,114,__uint64_t)

actually produce different ioctl numbers? If so, then I don't 
understand how the kernel can continue to offer the old/invalid 
interface when the new _IOR macro won't accept the first version any 
longer.