[PATCH] Staging: comedidev.h comedi_lrange should be const struct

[PATCH] Staging: comedidev.h comedi_lrange should be const struct

[Arthur Brainville (Ybalrid)]

According to checkpatch.pl, comedi_lrange should be declared as `const
struct` instead of `struct` in driver/staging/comedidev.h

Signed-off-by: Arthur Brainville (Ybalrid) <ybalrid@ybalrid.info>
---
 drivers/staging/comedi/comedidev.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
index 1bb9986f865e..82df090783b5 100644
--- a/drivers/staging/comedi/comedidev.h
+++ b/drivers/staging/comedi/comedidev.h
@@ -623,7 +623,7 @@ extern const struct comedi_lrange range_unknown;
  * There may also be a flag that indicates the minimum and maximum are merely
  * scale factors for an unknown, external reference.
  */
-struct comedi_lrange {
+const struct comedi_lrange {
 	int length;
 	struct comedi_krange range[];
 };
-- 
2.12.2

Re: [PATCH] Staging: comedidev.h comedi_lrange should be const struct

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 3473 bytes --]

Hi Arthur,

[auto build test WARNING on staging/staging-testing]
[also build test WARNING on v4.11-rc5 next-20170407]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Arthur-Brainville-Ybalrid/Staging-comedidev-h-comedi_lrange-should-be-const-struct/20170409-224503
config: x86_64-allyesdebian (attached as .config)
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   In file included from drivers/staging/comedi/comedi_fops.c:34:0:
>> drivers/staging/comedi/comedidev.h:629:1: warning: useless type qualifier in empty declaration
    };
    ^

vim +629 drivers/staging/comedi/comedidev.h

ed9eccbe8 David Schleef               2008-11-04  613  #define range_digital		range_unipolar5
ed9eccbe8 David Schleef               2008-11-04  614  
5459bc128 Ian Abbott                  2015-09-21  615  /**
5459bc128 Ian Abbott                  2015-09-21  616   * struct comedi_lrange - Describes a COMEDI range table
5459bc128 Ian Abbott                  2015-09-21  617   * @length: Number of entries in the range table.
5459bc128 Ian Abbott                  2015-09-21  618   * @range: Array of &struct comedi_krange, one for each range.
5459bc128 Ian Abbott                  2015-09-21  619   *
5459bc128 Ian Abbott                  2015-09-21  620   * Each element of @range[] describes the minimum and maximum physical range
5459bc128 Ian Abbott                  2015-09-21  621   * range and the type of units.  Typically, the type of unit is %UNIT_volt
5459bc128 Ian Abbott                  2015-09-21  622   * (i.e. volts) and the minimum and maximum are in millionths of a volt.
5459bc128 Ian Abbott                  2015-09-21  623   * There may also be a flag that indicates the minimum and maximum are merely
5459bc128 Ian Abbott                  2015-09-21  624   * scale factors for an unknown, external reference.
5459bc128 Ian Abbott                  2015-09-21  625   */
540e454c2 Arthur Brainville (Ybalrid  2017-04-09  626) const struct comedi_lrange {
ed9eccbe8 David Schleef               2008-11-04  627  	int length;
3358a0ca2 Cheah Kok Cheong            2016-12-22  628  	struct comedi_krange range[];
ed9eccbe8 David Schleef               2008-11-04 @629  };
ed9eccbe8 David Schleef               2008-11-04  630  
42e558399 Ian Abbott                  2015-09-21  631  /**
42e558399 Ian Abbott                  2015-09-21  632   * comedi_range_is_bipolar() - Test if subdevice range is bipolar
42e558399 Ian Abbott                  2015-09-21  633   * @s: COMEDI subdevice.
42e558399 Ian Abbott                  2015-09-21  634   * @range: Index of range within a range table.
42e558399 Ian Abbott                  2015-09-21  635   *
42e558399 Ian Abbott                  2015-09-21  636   * Tests whether a range is bipolar by checking whether its minimum value
42e558399 Ian Abbott                  2015-09-21  637   * is negative.

:::::: The code at line 629 was first introduced by commit
:::::: ed9eccbe8970f6eedc1b978c157caf1251a896d4 Staging: add comedi core

:::::: TO: David Schleef <ds@schleef.org>
:::::: CC: Greg Kroah-Hartman <gregkh@suse.de>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 38598 bytes --]

Re: [PATCH] Staging: comedidev.h comedi_lrange should be const struct

[Greg KH]

On Sun, Apr 09, 2017 at 04:28:12PM +0200, Arthur Brainville (Ybalrid) wrote:
> According to checkpatch.pl, comedi_lrange should be declared as `const
> struct` instead of `struct` in driver/staging/comedidev.h
> 
> Signed-off-by: Arthur Brainville (Ybalrid) <ybalrid@ybalrid.info>
> ---
>  drivers/staging/comedi/comedidev.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
> index 1bb9986f865e..82df090783b5 100644
> --- a/drivers/staging/comedi/comedidev.h
> +++ b/drivers/staging/comedi/comedidev.h
> @@ -623,7 +623,7 @@ extern const struct comedi_lrange range_unknown;
>   * There may also be a flag that indicates the minimum and maximum are merely
>   * scale factors for an unknown, external reference.
>   */
> -struct comedi_lrange {
> +const struct comedi_lrange {
>  	int length;
>  	struct comedi_krange range[];
>  };

Huh?  Please explain how this change is correct.

greg k-h

Re: [PATCH] Staging: comedidev.h comedi_lrange should be const struct

[kbuild test robot]

Hi Arthur,

[auto build test WARNING on staging/staging-testing]
[also build test WARNING on v4.11-rc6 next-20170407]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Arthur-Brainville-Ybalrid/Staging-comedidev-h-comedi_lrange-should-be-const-struct/20170409-224503
config: x86_64-allmodconfig
compiler: gcc-6 (Debian 6.2.0-3) 6.2.0 20160901
reproduce:
        make ARCH=x86_64  allmodconfig
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):


vim +629 drivers/staging/comedi/drivers/../comedidev.h

ed9eccbe8 David Schleef               2008-11-04  613  #define range_digital		range_unipolar5
ed9eccbe8 David Schleef               2008-11-04  614  
5459bc128 Ian Abbott                  2015-09-21  615  /**
5459bc128 Ian Abbott                  2015-09-21  616   * struct comedi_lrange - Describes a COMEDI range table
5459bc128 Ian Abbott                  2015-09-21  617   * @length: Number of entries in the range table.
5459bc128 Ian Abbott                  2015-09-21  618   * @range: Array of &struct comedi_krange, one for each range.
5459bc128 Ian Abbott                  2015-09-21  619   *
5459bc128 Ian Abbott                  2015-09-21  620   * Each element of @range[] describes the minimum and maximum physical range
5459bc128 Ian Abbott                  2015-09-21  621   * range and the type of units.  Typically, the type of unit is %UNIT_volt
5459bc128 Ian Abbott                  2015-09-21  622   * (i.e. volts) and the minimum and maximum are in millionths of a volt.
5459bc128 Ian Abbott                  2015-09-21  623   * There may also be a flag that indicates the minimum and maximum are merely
5459bc128 Ian Abbott                  2015-09-21  624   * scale factors for an unknown, external reference.
5459bc128 Ian Abbott                  2015-09-21  625   */
540e454c2 Arthur Brainville (Ybalrid  2017-04-09  626) const struct comedi_lrange {
ed9eccbe8 David Schleef               2008-11-04  627  	int length;
3358a0ca2 Cheah Kok Cheong            2016-12-22  628  	struct comedi_krange range[];
ed9eccbe8 David Schleef               2008-11-04 @629  };
ed9eccbe8 David Schleef               2008-11-04  630  
42e558399 Ian Abbott                  2015-09-21  631  /**
42e558399 Ian Abbott                  2015-09-21  632   * comedi_range_is_bipolar() - Test if subdevice range is bipolar
42e558399 Ian Abbott                  2015-09-21  633   * @s: COMEDI subdevice.
42e558399 Ian Abbott                  2015-09-21  634   * @range: Index of range within a range table.
42e558399 Ian Abbott                  2015-09-21  635   *
42e558399 Ian Abbott                  2015-09-21  636   * Tests whether a range is bipolar by checking whether its minimum value
42e558399 Ian Abbott                  2015-09-21  637   * is negative.

:::::: The code at line 629 was first introduced by commit
:::::: ed9eccbe8970f6eedc1b978c157caf1251a896d4 Staging: add comedi core

:::::: TO: David Schleef <ds@schleef.org>
:::::: CC: Greg Kroah-Hartman <gregkh@suse.de>

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[PATCH] checkpatch: Avoid suggesting struct definitions should be const

[Joe Perches]

Many structs are generally used const and there is a known list
of these structs.

struct definitions should not be generally be declared const.

Add a test for the lack of an open brace immediately after the
struct to avoid definitions.

This avoids the false positive "struct foo should normally be const"
message only when the open brace is on the same line as the definition.

Signed-off-by: Joe Perches <joe@perches.com>
---
 scripts/checkpatch.pl | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 089c974aa3a5..3a1cb9d7474e 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6090,11 +6090,11 @@ sub process {
 		}
 
 # check for various structs that are normally const (ops, kgdb, device_tree)
+# and avoid what seem like struct definitions 'struct foo {'
 		if ($line !~ /\bconst\b/ &&
-		    $line =~ /\bstruct\s+($const_structs)\b/) {
+		    $line =~ /\bstruct\s+($const_structs)\b(?!\s*\{)/) {
 			WARN("CONST_STRUCT",
-			     "struct $1 should normally be const\n" .
-				$herecurr);
+			     "struct $1 should normally be const\n" . $herecurr);
 		}
 
 # use of NR_CPUS is usually wrong
-- 
2.10.0.rc2.1.g053435c

Re: [PATCH] checkpatch: Avoid suggesting struct definitions should be const

[Arthur Brainville (Ybalrid)]

On Mon, Apr 10, 2017 at 10:45:55AM -0700, Joe Perches wrote:
> Many structs are generally used const and there is a known list
> of these structs.
> 
> struct definitions should not be generally be declared const.
> 
> Add a test for the lack of an open brace immediately after the
> struct to avoid definitions.
> 
> This avoids the false positive "struct foo should normally be const"
> message only when the open brace is on the same line as the definition.
> 
> Signed-off-by: Joe Perches <joe@perches.com>
> ---
>  scripts/checkpatch.pl | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 089c974aa3a5..3a1cb9d7474e 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -6090,11 +6090,11 @@ sub process {
>  		}
>  
>  # check for various structs that are normally const (ops, kgdb, device_tree)
> +# and avoid what seem like struct definitions 'struct foo {'
>  		if ($line !~ /\bconst\b/ &&
> -		    $line =~ /\bstruct\s+($const_structs)\b/) {
> +		    $line =~ /\bstruct\s+($const_structs)\b(?!\s*\{)/) {
>  			WARN("CONST_STRUCT",
> -			     "struct $1 should normally be const\n" .
> -				$herecurr);
> +			     "struct $1 should normally be const\n" . $herecurr);
>  		}
>  
>  # use of NR_CPUS is usually wrong
> -- 
> 2.10.0.rc2.1.g053435c
>

Oh, right... Everything makes sence now!

That output from checkpatch was confusing. Well, at least for that
little newbie that got the weird idea to send a "fix" on some comedi 
driver code (me).

(I have to say, that was an interesting experience, and if me sending
that patch made Joe Perches improve checkpatch a tiny little bit, it
wasn't *that* useless... I just hope I did not annoy people too much)


Obviusly, the patch I sent about that staging comedi driver should be
ignored. I'll be a bit more careful when looking at these thing, and 
recheck with the coding-style part of the doc.

Regards,
Arthur Brainville

Re: [PATCH] Staging: comedidev.h comedi_lrange should be const struct

[Arthur Brainville (Ybalrid)]

On Mon, Apr 10, 2017 at 10:01:05PM +0200, Greg KH wrote:
> On Mon, Apr 10, 2017 at 05:25:49PM +0200, Arthur Brainville wrote:
> > On Sun, Apr 09, 2017 at 09:02:03PM +0200, Greg KH wrote:
> > > On Sun, Apr 09, 2017 at 04:28:12PM +0200, Arthur Brainville (Ybalrid) wrote:
> > > > According to checkpatch.pl, comedi_lrange should be declared as `const
> > > > struct` instead of `struct` in driver/staging/comedidev.h
> > > >
> > > > Signed-off-by: Arthur Brainville (Ybalrid) <ybalrid@ybalrid.info>
> > > > ---
> > > >  drivers/staging/comedi/comedidev.h | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
> > > > index 1bb9986f865e..82df090783b5 100644
> > > > --- a/drivers/staging/comedi/comedidev.h
> > > > +++ b/drivers/staging/comedi/comedidev.h
> > > > @@ -623,7 +623,7 @@ extern const struct comedi_lrange range_unknown;
> > > >   * There may also be a flag that indicates the minimum and maximum are merely
> > > >   * scale factors for an unknown, external reference.
> > > >   */
> > > > -struct comedi_lrange {
> > > > +const struct comedi_lrange {
> > > >  	int length;
> > > >  	struct comedi_krange range[];
> > > >  };
> > > 
> > > Huh?  Please explain how this change is correct.
> > > 
> > > greg k-h
> > 
> > First of all, thanks for taking the time to reply!
> > Well, sorry if I did something wrong, I'm a newbie here, so let me
> > explain:
> > 
> > When checking a bunch of files with /script/checkpatch.pl -f on the
> > staging directory, it gave me this output:
> > 
> > > WARNING: struct comedi_lrange should normally be const
> > > #626: FILE: drivers/staging/comedi/comedidev.h:626:
> > > +struct comedi_lrange {
> > > 
> > > total: 0 errors, 1 warnings, 6 checks, 1043 lines checked
> > > 
> > > NOTE: For some of the reported defects, checkpatch may be able to
> > >      mechanically convert to the typical style using --fix or
> > >      --fix-inplace.
> > 
> > For this specific header.
> > 
> > Declaring it as const struct fixes that coding style warning, and
> > doesn't break the build but, AFAIK isn't actually meaningfull since it's
> > declaring a struct, but not any variable of type "comedi_lrange"
> > at this point. And it built fine.
> > I was watching an old talk (from you) about how you can send a patch to
> > correct this kind of little things, so I tried.
> > 
> > Looking further into it, it seems that this change makes GCC trigger the
> > following warning in any file that #include it :
> > > In file included from drivers/staging/comedi//comedi_usb.h:24:0,
> > >                 from drivers/staging/comedi//comedi_usb.c:21:
> > >                 drivers/staging/comedi//comedidev.h:629:1: warning:
> > >                 useless type qualifier in empty declaration
> > >                  };
> > 
> > So, probably not good?
> 
> You should always test-build your patches, and they can never add new
> kernel warnings to the build, that's not allowed at all.  So please do
> that next time, it should have shown you that this was not a good
> change.
> 
> And as you have found out, checkpatch.pl is a dumb tool, you still have
> to think when you use it.  And if you know C, you will know that the
> change you made makes no sense at all :)
> 
> thanks,
> 
> greg k-h

Lesson learned!

(It did build. But well, I don't know what I was thinking not paying
attentions to theses warning. Shame on me!)

Thank you again for your patience Greg :)

Arthur Brainville

Re: [PATCH] Staging: comedidev.h comedi_lrange should be const struct

[Greg KH]

On Mon, Apr 10, 2017 at 05:25:49PM +0200, Arthur Brainville wrote:
> On Sun, Apr 09, 2017 at 09:02:03PM +0200, Greg KH wrote:
> > On Sun, Apr 09, 2017 at 04:28:12PM +0200, Arthur Brainville (Ybalrid) wrote:
> > > According to checkpatch.pl, comedi_lrange should be declared as `const
> > > struct` instead of `struct` in driver/staging/comedidev.h
> > >
> > > Signed-off-by: Arthur Brainville (Ybalrid) <ybalrid@ybalrid.info>
> > > ---
> > >  drivers/staging/comedi/comedidev.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
> > > index 1bb9986f865e..82df090783b5 100644
> > > --- a/drivers/staging/comedi/comedidev.h
> > > +++ b/drivers/staging/comedi/comedidev.h
> > > @@ -623,7 +623,7 @@ extern const struct comedi_lrange range_unknown;
> > >   * There may also be a flag that indicates the minimum and maximum are merely
> > >   * scale factors for an unknown, external reference.
> > >   */
> > > -struct comedi_lrange {
> > > +const struct comedi_lrange {
> > >  	int length;
> > >  	struct comedi_krange range[];
> > >  };
> > 
> > Huh?  Please explain how this change is correct.
> > 
> > greg k-h
> 
> First of all, thanks for taking the time to reply!
> Well, sorry if I did something wrong, I'm a newbie here, so let me
> explain:
> 
> When checking a bunch of files with /script/checkpatch.pl -f on the
> staging directory, it gave me this output:
> 
> > WARNING: struct comedi_lrange should normally be const
> > #626: FILE: drivers/staging/comedi/comedidev.h:626:
> > +struct comedi_lrange {
> > 
> > total: 0 errors, 1 warnings, 6 checks, 1043 lines checked
> > 
> > NOTE: For some of the reported defects, checkpatch may be able to
> >      mechanically convert to the typical style using --fix or
> >      --fix-inplace.
> 
> For this specific header.
> 
> Declaring it as const struct fixes that coding style warning, and
> doesn't break the build but, AFAIK isn't actually meaningfull since it's
> declaring a struct, but not any variable of type "comedi_lrange"
> at this point. And it built fine.
> I was watching an old talk (from you) about how you can send a patch to
> correct this kind of little things, so I tried.
> 
> Looking further into it, it seems that this change makes GCC trigger the
> following warning in any file that #include it :
> > In file included from drivers/staging/comedi//comedi_usb.h:24:0,
> >                 from drivers/staging/comedi//comedi_usb.c:21:
> >                 drivers/staging/comedi//comedidev.h:629:1: warning:
> >                 useless type qualifier in empty declaration
> >                  };
> 
> So, probably not good?

You should always test-build your patches, and they can never add new
kernel warnings to the build, that's not allowed at all.  So please do
that next time, it should have shown you that this was not a good
change.

And as you have found out, checkpatch.pl is a dumb tool, you still have
to think when you use it.  And if you know C, you will know that the
change you made makes no sense at all :)

thanks,

greg k-h

Re: [PATCH] Staging: comedidev.h comedi_lrange should be const struct

[Arthur Brainville]

On Sun, Apr 09, 2017 at 09:02:03PM +0200, Greg KH wrote:
> On Sun, Apr 09, 2017 at 04:28:12PM +0200, Arthur Brainville (Ybalrid) wrote:
> > According to checkpatch.pl, comedi_lrange should be declared as `const
> > struct` instead of `struct` in driver/staging/comedidev.h
> >
> > Signed-off-by: Arthur Brainville (Ybalrid) <ybalrid@ybalrid.info>
> > ---
> >  drivers/staging/comedi/comedidev.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/comedi/comedidev.h b/drivers/staging/comedi/comedidev.h
> > index 1bb9986f865e..82df090783b5 100644
> > --- a/drivers/staging/comedi/comedidev.h
> > +++ b/drivers/staging/comedi/comedidev.h
> > @@ -623,7 +623,7 @@ extern const struct comedi_lrange range_unknown;
> >   * There may also be a flag that indicates the minimum and maximum are merely
> >   * scale factors for an unknown, external reference.
> >   */
> > -struct comedi_lrange {
> > +const struct comedi_lrange {
> >  	int length;
> >  	struct comedi_krange range[];
> >  };
>
> Huh?  Please explain how this change is correct.
>
> greg k-h

First of all, thanks for taking the time to reply!
Well, sorry if I did something wrong, I'm a newbie here, so let me
explain:

When checking a bunch of files with /script/checkpatch.pl -f on the
staging directory, it gave me this output:

> WARNING: struct comedi_lrange should normally be const
> #626: FILE: drivers/staging/comedi/comedidev.h:626:
> +struct comedi_lrange {
>
> total: 0 errors, 1 warnings, 6 checks, 1043 lines checked
>
> NOTE: For some of the reported defects, checkpatch may be able to
>      mechanically convert to the typical style using --fix or
>      --fix-inplace.

For this specific header.

Declaring it as const struct fixes that coding style warning, and
doesn't break the build but, AFAIK isn't actually meaningfull since it's 
declaring a struct, but not any variable of type "comedi_lrange"
at this point. And it built fine.
I was watching an old talk (from you) about how you can send a patch to
correct this kind of little things, so I tried.

Looking further into it, it seems that this change makes GCC trigger the
following warning in any file that #include it :
> In file included from drivers/staging/comedi//comedi_usb.h:24:0,
>                 from drivers/staging/comedi//comedi_usb.c:21:
>                 drivers/staging/comedi//comedidev.h:629:1: warning:
>                 useless type qualifier in empty declaration
>                  };

So, probably not good?
Like I said  here the `const` qualifier doen't change anything, you 
could create a `struct comedi_lrange` variable with some initialization,
and change it later, it will not be const, unless declared so at that
point.

It was just to make this file pass the checkpatch perl script without
warning, but it makes the staging comedi driver compile with warnings.

It doesn't change anything "functionally", if you see what I mean.