RE: [PATCH] incorrect use of sizeof() in ioctl definitions

[Tian, Kevin]

> Andries Brouwer [mailto:aebr@xxxxxxxxxx] wrote:
> On Tue, Sep 30, 2003 at 11:25:56PM +0100, Matthew Wilcox wrote:
> > On Tue, Sep 30, 2003 at 02:08:05PM -0700, Andrew Morton wrote:
> > > Arun Sharma <arun.sharma@xxxxxxxxx> wrote:
> > > >
> > > > Some drivers seem to use macros such as _IOR/_IOW in a way that
ends
> up
> > > > calling the sizeof() operator twice. For eg:
> > > >
> > > > -#define FBIO_ATY128_GET_MIRROR	_IOR('@', 1, sizeof(__u32*))
> > > > +#define FBIO_ATY128_GET_MIRROR	_IOR('@', 1, __u32*)
> 
> But this changes the define. You want
> 
> #define FBIO_ATY128_GET_MIRROR	_IOR_BAD('@', 1, __u32*)

	Maybe I got something wrong, but could someone please help me to
understand why introduce _IOR_BAD here? Thanks first! :)

	IMO, the birth of new ioctl definition convention considers
"size" of argument as a part, so we should conform to this rule.
_IOR_BAD is no different as old one <_IOR('@', 1, sizeof(__u32*))>,
which expands as sizeof(sizeof(__32*)) and actually assume temp result
of internal sizeof as the argument. Of course this didn't reflect the
true point and we should change the definition. :)

	Also I'm confused about the modification about using size_t to
replace sizeof(). Take MATROXFB_SET_OUTPUT_MODE for example:

(old)	#define MATROXFB_SET_OUTPUT_MODE
_IOW('n',0xFA,sizeof(struct matroxioc_output_mode))
(now)	#define MATROXFB_SET_OUTPUT_MODE        _IOW('n',0xFA,size_t)

	The size of matroxioc_output_mode is 8 bytes on all platforms,
however size_t will be calculated as 4 bytes on 32bit arch and 8 bytes
on 64bit arch. So this is also like using sizeof(), which imposes the
difference between 32bit ioctl number and 64bit ioctl number. However in
standard manner, I mean:
	#define MATROXFB_SET_OUTPUT_MODE        _IOW('n',0xFA,struct
matroxioc_output_mode)
 	The value should be identical on all platforms, which save our
efforts to do useless conversion when running 32bit apps on 64bit
platform.

	The most important is: to use sizeof() or size_t here both
messed the ioctl definition, which violate the initial motivation of
_IO**, is it?

> Something else we should do is to change all occurrences of 'size'
> here into 'argtype'. All this nonsense came because of the bad choice
> of identifier.
	Agree. The inaccurate name here confused us... :)
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/