Re: [PATCH] fixed a macro coding style issue

[Dmitry Torokhov]

On Tue, Jul 24, 2012 at 11:36:24PM -0700, Dmitry Torokhov wrote:
> On Wed, Jul 25, 2012 at 07:15:12AM +0100, Al Viro wrote:
> > On Tue, Jul 24, 2012 at 10:37:55PM -0700, Dmitry Torokhov wrote:
> > > On Wed, Jul 25, 2012 at 01:20:56PM +0800, Baodong Chen wrote:
> > > > Fixed a coding style issue in driver/input/input.c
> > > > 
> > > > Signed-off-by: Baodong Chen <chenbdchenbd@xxxxxxxxx>
> > > > ---
> > > >  drivers/input/input.c |    6 ++++--
> > > >  1 files changed, 4 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/drivers/input/input.c b/drivers/input/input.c
> > > > index 8921c61..c96e983 100644
> > > > --- a/drivers/input/input.c
> > > > +++ b/drivers/input/input.c
> > > > @@ -845,11 +845,13 @@ int input_set_keycode(struct input_dev *dev,
> > > >  EXPORT_SYMBOL(input_set_keycode);
> > > >  
> > > >  #define MATCH_BIT(bit, max) \
> > > > +	do { \
> > > >  		for (i = 0; i < BITS_TO_LONGS(max); i++) \
> > > >  			if ((id->bit[i] & dev->bit[i]) != id->bit[i]) \
> > > >  				break; \
> > > > -		if (i != BITS_TO_LONGS(max)) \
> > > > -			continue;
> > > > +			if (i != BITS_TO_LONGS(max)) \
> > > > +				continue; \
> > > > +	} while (0)
> > > 
> > > This changes semantics. While current implementation of MATCH_BIT might
> > > not be great style, it is not supposed to be used outside of
> > > input_match_device(), and the replacement is completely broken.
> > 
> > Replacement is certainly completely broken, but "might not be great style"
> > is quite an understatement.  Everything else aside, it's too obfuscated
> > and ugly for anything outside of IOCCC and too verbose for IOCCC.
> > 
> > Damnit, at least turn that into
> > static inline int is_subset(unsigned long *bitmap1, unsigned long *bitmap2, size_t bits)
> > {
> > 	int i;
> > 	for (i = BITS_TO_LONGS(bits); i; bitmap1++, bitmap2++, i--)
> > 		if ((*bitmap1 & *bitmap2) != *bitmap1)
> > 			return 0;
> > 	return 1;
> > }
> > and just before your loop
> > /* ignore ones that don't have bits required by id */
> > #define MATCH_BIT(array, bits) if (!is_subset(id->array, dev->array, bits)) continue;
> 
> Hmm, we already have bitmap_subset(), I think we can simply use it.
> 
> > with #undef MATCH_BIT right after the loop, to make it damn clean that it's local.
> > And frankly, I'd consider expanding that variant and killing the macro off.
> > Macros that affect control flow are vile and actively confusing for reader.
> 
> I agree. In my defense it is quite old code...

So how about the patch below?

-- 
Dmitry

Input: get rid of MATCH_BIT() macro

From: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>

MATCH_BIT() is ugly and stupid, we have much nicer bitmap_subset() which
does the same and does not hide control flow.

Reported-by: Baodong Chen <chenbdchenbd@xxxxxxxxx>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
---

 drivers/input/input.c |   43 ++++++++++++++++++++++++++-----------------
 1 file changed, 26 insertions(+), 17 deletions(-)


diff --git a/drivers/input/input.c b/drivers/input/input.c
index 8921c61..768e46b 100644
--- a/drivers/input/input.c
+++ b/drivers/input/input.c
@@ -844,18 +844,10 @@ int input_set_keycode(struct input_dev *dev,
 }
 EXPORT_SYMBOL(input_set_keycode);
 
-#define MATCH_BIT(bit, max) \
-		for (i = 0; i < BITS_TO_LONGS(max); i++) \
-			if ((id->bit[i] & dev->bit[i]) != id->bit[i]) \
-				break; \
-		if (i != BITS_TO_LONGS(max)) \
-			continue;
-
 static const struct input_device_id *input_match_device(struct input_handler *handler,
 							struct input_dev *dev)
 {
 	const struct input_device_id *id;
-	int i;
 
 	for (id = handler->id_table; id->flags || id->driver_info; id++) {
 
@@ -875,15 +867,32 @@ static const struct input_device_id *input_match_device(struct input_handler *ha
 			if (id->version != dev->id.version)
 				continue;
 
-		MATCH_BIT(evbit,  EV_MAX);
-		MATCH_BIT(keybit, KEY_MAX);
-		MATCH_BIT(relbit, REL_MAX);
-		MATCH_BIT(absbit, ABS_MAX);
-		MATCH_BIT(mscbit, MSC_MAX);
-		MATCH_BIT(ledbit, LED_MAX);
-		MATCH_BIT(sndbit, SND_MAX);
-		MATCH_BIT(ffbit,  FF_MAX);
-		MATCH_BIT(swbit,  SW_MAX);
+		if (!bitmap_subset(id->evbit, dev->evbit, EV_MAX))
+			continue;
+
+		if (!bitmap_subset(id->keybit, dev->keybit, KEY_MAX))
+			continue;
+
+		if (!bitmap_subset(id->relbit, dev->relbit, REL_MAX))
+			continue;
+
+		if (!bitmap_subset(id->absbit, dev->absbit, ABS_MAX))
+			continue;
+
+		if (!bitmap_subset(id->mscbit, dev->mscbit, MSC_MAX))
+			continue;
+
+		if (!bitmap_subset(id->ledbit, dev->ledbit, LED_MAX))
+			continue;
+
+		if (!bitmap_subset(id->sndbit, dev->sndbit, SND_MAX))
+			continue;
+
+		if (!bitmap_subset(id->ffbit, dev->ffbit, FF_MAX))
+			continue;
+
+		if (!bitmap_subset(id->swbit, dev->swbit, SW_MAX))
+			continue;
 
 		if (!handler->match || handler->match(handler, dev))
 			return id;
--
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