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

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Message-ID: <Y4RwXSs9ha0zepxZ@kadam>
Date:   Mon, 28 Nov 2022 11:25:01 +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 01:51:58PM +0530, Deepak R Varma wrote:
> On Mon, Nov 28, 2022 at 10:50:19AM +0300, Dan Carpenter wrote:
> > 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:
> 
> Thank you Dan. This takes me back to the very first version of this patch. I
> will send in the clean up.

Don't just send what I sent you, look around and try to see if there are
other issues with the code.

regards,
dan carpenter