linux-kernel - Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with DECLARE_FLEX

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Message-ID: <Y4RoOxgo76Hc5RRP@kadam>
Date:   Mon, 28 Nov 2022 10:50:19 +0300
From:   Dan Carpenter <error27@...il.com>
To:     Deepak R Varma <drv@...lo.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        gustavoars@...nel.org
Subject: Re: [PATCH] staging: wlan-ng: Replace zero-length arrays with
 DECLARE_FLEX_ARRAY() helper

On Mon, Nov 28, 2022 at 01:15:43PM +0530, Deepak R Varma wrote:
> On Sat, Nov 19, 2022 at 08:08:15PM +0530, Deepak R Varma wrote:
> > On Thu, Nov 17, 2022 at 07:03:21PM +0100, Greg Kroah-Hartman wrote:
> > > On Thu, Nov 17, 2022 at 06:50:55PM +0530, Deepak R Varma wrote:
> > > > On Thu, Nov 17, 2022 at 01:54:49PM +0100, Greg Kroah-Hartman wrote:
> > > > > On Thu, Nov 17, 2022 at 03:48:45PM +0530, Deepak R Varma wrote:
> > > > > >
> > > > > >  struct hfa384x_pdr_refdac_measurements {
> > > > > > -	u16 value[0];
> > > > > > +	DECLARE_FLEX_ARRAY(u16, value);
> > > > > >  } __packed;
> > > > >
> > > > > Why?  This structure is never used anywhere, right?  So why is this
> > > > > needed to be changed and not just removed entirely?  Same for the other
> > > > > structures in this patch.
> > > >
> > > > Hello Greg,
> > > > I am unable to confirm that these structures are truly not needed in the absence
> > > > if a real device based testing. I could only validate that using the compile
> > > > build and driver loading.
> > >
> > > Think this through, if no one is actually using this structure, and it
> > > is of 0 size, then do you think it is being used?
> >
> > Hello Greg,
> > I did not find any memory allocation for these zero length array structures.
> > Also, the union or its enclosing structure do not appear to access the members.
> > Hence I am leaning towards concluding that these zero length array structures do
> > not appear to be necessary.
> >
> > There are a few other structures that are part of the same union, however, they
> > too do not appear to be used for accessing the memory assigned to the union [or
> > its enclosing structure]. I think most of the members of these unions can be
> > replaced by one max size structure of this union [e.g. struct
> > hfa384x_pdr_mkk_measurements].
> >
> > Could you please comment if I am reading the code right?
> >
> > For your quick reference, the zero length structure declaration are online 963
> > whereas the union is on line number 1080 of the file drivers/staging/wlan-ng/hfa384x.h
> 
> Hello Greg,
> can you please suggest how should I approach this clean-up/correction?
> 

Like this:

diff --git a/drivers/staging/wlan-ng/hfa384x.h b/drivers/staging/wlan-ng/hfa384x.h
index 0611e37df6ac..6a3df58c9e9c 100644
--- a/drivers/staging/wlan-ng/hfa384x.h
+++ b/drivers/staging/wlan-ng/hfa384x.h
@@ -959,10 +959,6 @@ struct hfa384x_pdr_nicid {
 	u16 minor;
 } __packed;
 
-struct hfa384x_pdr_refdac_measurements {
-	u16 value[0];
-} __packed;
-
 struct hfa384x_pdr_vgdac_measurements {
 	u16 value[0];
 } __packed;
@@ -1077,7 +1073,6 @@ struct hfa384x_pdrec {
 		struct hfa384x_pdr_mfisuprange mfisuprange;
 		struct hfa384x_pdr_cfisuprange cfisuprange;
 		struct hfa384x_pdr_nicid nicid;
-		struct hfa384x_pdr_refdac_measurements refdac_measurements;
 		struct hfa384x_pdr_vgdac_measurements vgdac_measurements;
 		struct hfa384x_pdr_level_comp_measurements level_compc_measurements;
 		struct hfa384x_pdr_mac_address mac_address;