[PATCH] btrfs: Fix a C compliance issue

[PATCH] btrfs: Fix a C compliance issue

[Bart Van Assche]

The C programming language does not allow to use preprocessor statements
inside macro arguments (pr_info() is defined as a macro). Hence rework
the pr_info() statement in btrfs_print_mod_info() such that it becomes
compliant. This patch allows tools like sparse to analyze the BTRFS
source code.

Fixes: 62e855771dac ("btrfs: convert printk(KERN_* to use pr_* calls")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: David Sterba <dsterba@suse.com>
---
 fs/btrfs/super.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 81107ad49f3a..dd4980df5b8e 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2369,7 +2369,7 @@ static __cold void btrfs_interface_exit(void)
 
 static void __init btrfs_print_mod_info(void)
 {
-	pr_info("Btrfs loaded, crc32c=%s"
+	static const char fmt[] = KERN_INFO "Btrfs loaded, crc32c=%s"
 #ifdef CONFIG_BTRFS_DEBUG
 			", debug=on"
 #endif
@@ -2382,8 +2382,8 @@ static void __init btrfs_print_mod_info(void)
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 			", ref-verify=on"
 #endif
-			"\n",
-			crc32c_impl());
+			"\n";
+	printk(fmt, crc32c_impl());
 }
 
 static int __init init_btrfs_fs(void)
-- 
2.17.0

Re: [PATCH] btrfs: Fix a C compliance issue

[Nikolay Borisov]

On 16.06.2018 01:36, Bart Van Assche wrote:
> The C programming language does not allow to use preprocessor statements
> inside macro arguments (pr_info() is defined as a macro). Hence rework
> the pr_info() statement in btrfs_print_mod_info() such that it becomes
> compliant. This patch allows tools like sparse to analyze the BTRFS
> source code.
> 
> Fixes: 62e855771dac ("btrfs: convert printk(KERN_* to use pr_* calls")
> Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
> Cc: Jeff Mahoney <jeffm@suse.com>
> Cc: David Sterba <dsterba@suse.com>
> ---
>  fs/btrfs/super.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 81107ad49f3a..dd4980df5b8e 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -2369,7 +2369,7 @@ static __cold void btrfs_interface_exit(void)
>  
>  static void __init btrfs_print_mod_info(void)
>  {
> -	pr_info("Btrfs loaded, crc32c=%s"
> +	static const char fmt[] = KERN_INFO "Btrfs loaded, crc32c=%s"
>  #ifdef CONFIG_BTRFS_DEBUG
>  			", debug=on"
>  #endif
> @@ -2382,8 +2382,8 @@ static void __init btrfs_print_mod_info(void)
>  #ifdef CONFIG_BTRFS_FS_REF_VERIFY
>  			", ref-verify=on"
>  #endif
> -			"\n",
> -			crc32c_impl());
> +			"\n";
> +	printk(fmt, crc32c_impl());

I'd rather not see more printk being added. Nothing prevents from having
the fmt string being passed to pr_info.
>  }
>  
>  static int __init init_btrfs_fs(void)
> 

Re: [PATCH] btrfs: Fix a C compliance issue

[David Sterba]

On Sat, Jun 16, 2018 at 01:28:13PM +0300, Nikolay Borisov wrote:
> 
> 
> On 16.06.2018 01:36, Bart Van Assche wrote:
> > The C programming language does not allow to use preprocessor statements
> > inside macro arguments (pr_info() is defined as a macro). Hence rework
> > the pr_info() statement in btrfs_print_mod_info() such that it becomes
> > compliant. This patch allows tools like sparse to analyze the BTRFS
> > source code.
> > 
> > Fixes: 62e855771dac ("btrfs: convert printk(KERN_* to use pr_* calls")
> > Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
> > Cc: Jeff Mahoney <jeffm@suse.com>
> > Cc: David Sterba <dsterba@suse.com>
> > ---
> >  fs/btrfs/super.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> > index 81107ad49f3a..dd4980df5b8e 100644
> > --- a/fs/btrfs/super.c
> > +++ b/fs/btrfs/super.c
> > @@ -2369,7 +2369,7 @@ static __cold void btrfs_interface_exit(void)
> >  
> >  static void __init btrfs_print_mod_info(void)
> >  {
> > -	pr_info("Btrfs loaded, crc32c=%s"
> > +	static const char fmt[] = KERN_INFO "Btrfs loaded, crc32c=%s"
> >  #ifdef CONFIG_BTRFS_DEBUG
> >  			", debug=on"
> >  #endif
> > @@ -2382,8 +2382,8 @@ static void __init btrfs_print_mod_info(void)
> >  #ifdef CONFIG_BTRFS_FS_REF_VERIFY
> >  			", ref-verify=on"
> >  #endif
> > -			"\n",
> > -			crc32c_impl());
> > +			"\n";
> > +	printk(fmt, crc32c_impl());
> 
> I'd rather not see more printk being added. Nothing prevents from having
> the fmt string being passed to pr_info.

So you mean to do

+	static const char fmt[] = "Btrfs loaded, crc32c=%s"
+	pr_info(fmt);

?

Re: [PATCH] btrfs: Fix a C compliance issue

[Nikolay Borisov]

On 18.06.2018 12:26, David Sterba wrote:
> On Sat, Jun 16, 2018 at 01:28:13PM +0300, Nikolay Borisov wrote:
>>
>>
>> On 16.06.2018 01:36, Bart Van Assche wrote:
>>> The C programming language does not allow to use preprocessor statements
>>> inside macro arguments (pr_info() is defined as a macro). Hence rework
>>> the pr_info() statement in btrfs_print_mod_info() such that it becomes
>>> compliant. This patch allows tools like sparse to analyze the BTRFS
>>> source code.
>>>
>>> Fixes: 62e855771dac ("btrfs: convert printk(KERN_* to use pr_* calls")
>>> Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
>>> Cc: Jeff Mahoney <jeffm@suse.com>
>>> Cc: David Sterba <dsterba@suse.com>
>>> ---
>>>  fs/btrfs/super.c | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
>>> index 81107ad49f3a..dd4980df5b8e 100644
>>> --- a/fs/btrfs/super.c
>>> +++ b/fs/btrfs/super.c
>>> @@ -2369,7 +2369,7 @@ static __cold void btrfs_interface_exit(void)
>>>  
>>>  static void __init btrfs_print_mod_info(void)
>>>  {
>>> -	pr_info("Btrfs loaded, crc32c=%s"
>>> +	static const char fmt[] = KERN_INFO "Btrfs loaded, crc32c=%s"
>>>  #ifdef CONFIG_BTRFS_DEBUG
>>>  			", debug=on"
>>>  #endif
>>> @@ -2382,8 +2382,8 @@ static void __init btrfs_print_mod_info(void)
>>>  #ifdef CONFIG_BTRFS_FS_REF_VERIFY
>>>  			", ref-verify=on"
>>>  #endif
>>> -			"\n",
>>> -			crc32c_impl());
>>> +			"\n";
>>> +	printk(fmt, crc32c_impl());
>>
>> I'd rather not see more printk being added. Nothing prevents from having
>> the fmt string being passed to pr_info.
> 
> So you mean to do
> 
> +	static const char fmt[] = "Btrfs loaded, crc32c=%s"
> +	pr_info(fmt);

Pretty much, something along the lines of

pr_info(fmt, crc32c_impl).

printk requires having the KERN_INFO in the format string, which I see
no point in doing, correct me if I'm wrong?
> 
> ?
> 

Re: [PATCH] btrfs: Fix a C compliance issue

[Bart Van Assche]

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On Mon, 2018-06-18 at 12:31 +0300, Nikolay Borisov wrote:
> On 18.06.2018 12:26, David Sterba wrote:
> > On Sat, Jun 16, 2018 at 01:28:13PM +0300, Nikolay Borisov wrote:
> > > I'd rather not see more printk being added. Nothing prevents from having
> > > the fmt string being passed to pr_info.
> > 
> > So you mean to do
> > 
> > +	static const char fmt[] = "Btrfs loaded, crc32c=%s"
> > +	pr_info(fmt);
> 
> Pretty much, something along the lines of
> 
> pr_info(fmt, crc32c_impl).
> 
> printk requires having the KERN_INFO in the format string, which I see
> no point in doing, correct me if I'm wrong?

You should know that what you proposed doesn't compile because pr_info()
relies on string concatenation and hence requires that its first argument is
a string constant instead of a const char pointer. Anyway, I will rework this
patch such that it uses pr_info() instead of printk().

Bart.


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Re: [PATCH] btrfs: Fix a C compliance issue

[David Sterba]

On Wed, Jun 20, 2018 at 04:44:54PM +0000, Bart Van Assche wrote:
> On Mon, 2018-06-18 at 12:31 +0300, Nikolay Borisov wrote:
> > On 18.06.2018 12:26, David Sterba wrote:
> > > On Sat, Jun 16, 2018 at 01:28:13PM +0300, Nikolay Borisov wrote:
> > > > I'd rather not see more printk being added. Nothing prevents from having
> > > > the fmt string being passed to pr_info.
> > > 
> > > So you mean to do
> > > 
> > > +	static const char fmt[] = "Btrfs loaded, crc32c=%s"
> > > +	pr_info(fmt);
> > 
> > Pretty much, something along the lines of
> > 
> > pr_info(fmt, crc32c_impl).
> > 
> > printk requires having the KERN_INFO in the format string, which I see
> > no point in doing, correct me if I'm wrong?
> 
> You should know that what you proposed doesn't compile because pr_info()
> relies on string concatenation and hence requires that its first argument is
> a string constant instead of a const char pointer. Anyway, I will rework this
> patch such that it uses pr_info() instead of printk().

Right, the pr_info(fmt,...) does not compile. The closest version I got to is
below. It does not look pretty, but I can't think of a better version right
now.

--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2369,7 +2369,8 @@ static __cold void btrfs_interface_exit(void)
 
 static void __init btrfs_print_mod_info(void)
 {
-       static const char fmt[] = KERN_INFO "Btrfs loaded, crc32c=%s"
+       static const char fmt1[] = "Btrfs loaded, crc32c=";
+       static const char fmt2[] =
 #ifdef CONFIG_BTRFS_DEBUG
                        ", debug=on"
 #endif
@@ -2383,7 +2384,7 @@ static void __init btrfs_print_mod_info(void)
                        ", ref-verify=on"
 #endif
                        "\n";
-       printk(fmt, crc32c_impl());
+       pr_info("%s%s%s", fmt1, crc32c_impl(), fmt2);
 }
 
 static int __init init_btrfs_fs(void)

Re: [PATCH] btrfs: Fix a C compliance issue

[Jeff Mahoney]

On 6/20/18 12:55 PM, David Sterba wrote:
> On Wed, Jun 20, 2018 at 04:44:54PM +0000, Bart Van Assche wrote:
>> On Mon, 2018-06-18 at 12:31 +0300, Nikolay Borisov wrote:
>>> On 18.06.2018 12:26, David Sterba wrote:
>>>> On Sat, Jun 16, 2018 at 01:28:13PM +0300, Nikolay Borisov wrote:
>>>>> I'd rather not see more printk being added. Nothing prevents from having
>>>>> the fmt string being passed to pr_info.
>>>>
>>>> So you mean to do
>>>>
>>>> +	static const char fmt[] = "Btrfs loaded, crc32c=%s"
>>>> +	pr_info(fmt);
>>>
>>> Pretty much, something along the lines of
>>>
>>> pr_info(fmt, crc32c_impl).
>>>
>>> printk requires having the KERN_INFO in the format string, which I see
>>> no point in doing, correct me if I'm wrong?
>>
>> You should know that what you proposed doesn't compile because pr_info()
>> relies on string concatenation and hence requires that its first argument is
>> a string constant instead of a const char pointer. Anyway, I will rework this
>> patch such that it uses pr_info() instead of printk().
> 
> Right, the pr_info(fmt,...) does not compile. The closest version I got to is
> below. It does not look pretty, but I can't think of a better version right
> now.
> 
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -2369,7 +2369,8 @@ static __cold void btrfs_interface_exit(void)
>  
>  static void __init btrfs_print_mod_info(void)
>  {
> -       static const char fmt[] = KERN_INFO "Btrfs loaded, crc32c=%s"
> +       static const char fmt1[] = "Btrfs loaded, crc32c=";
> +       static const char fmt2[] =
>  #ifdef CONFIG_BTRFS_DEBUG
>                         ", debug=on"
>  #endif
> @@ -2383,7 +2384,7 @@ static void __init btrfs_print_mod_info(void)
>                         ", ref-verify=on"
>  #endif
>                         "\n";
> -       printk(fmt, crc32c_impl());
> +       pr_info("%s%s%s", fmt1, crc32c_impl(), fmt2);
>  }
>  
>  static int __init init_btrfs_fs(void)

The shed should be yellow.

-Jeff

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 891cd2ed5dd4..57c9da0b459f 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2375,21 +2375,20 @@ static __cold void btrfs_interface_exit(void)

 static void __init btrfs_print_mod_info(void)
 {
-	pr_info("Btrfs loaded, crc32c=%s"
+	pr_info("Btrfs loaded, crc32c=%s", crc32c_impl());
 #ifdef CONFIG_BTRFS_DEBUG
-			", debug=on"
+	pr_cont(", debug=on");
 #endif
 #ifdef CONFIG_BTRFS_ASSERT
-			", assert=on"
+	pr_cont(", assert=on");
 #endif
 #ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
-			", integrity-checker=on"
+	pr_cont(", integrity-checker=on");
 #endif
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
-			", ref-verify=on"
+	pr_cont(", ref-verify=on")
 #endif
-			"\n",
-			crc32c_impl());
+	pr_cont("\n");
 }

 static int null_open(struct block_device *bdev, fmode_t mode)



-- 
Jeff Mahoney
SUSE Labs

Re: [PATCH] btrfs: Fix a C compliance issue

[Bart Van Assche]

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On Wed, 2018-06-20 at 13:19 -0400, Jeff Mahoney wrote:
> The shed should be yellow.
> 
> -Jeff
> 
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 891cd2ed5dd4..57c9da0b459f 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -2375,21 +2375,20 @@ static __cold void btrfs_interface_exit(void)
> 
>  static void __init btrfs_print_mod_info(void)
>  {
> -	pr_info("Btrfs loaded, crc32c=%s"
> +	pr_info("Btrfs loaded, crc32c=%s", crc32c_impl());
>  #ifdef CONFIG_BTRFS_DEBUG
> -			", debug=on"
> +	pr_cont(", debug=on");
>  #endif
>  #ifdef CONFIG_BTRFS_ASSERT
> -			", assert=on"
> +	pr_cont(", assert=on");
>  #endif
>  #ifdef CONFIG_BTRFS_FS_CHECK_INTEGRITY
> -			", integrity-checker=on"
> +	pr_cont(", integrity-checker=on");
>  #endif
>  #ifdef CONFIG_BTRFS_FS_REF_VERIFY
> -			", ref-verify=on"
> +	pr_cont(", ref-verify=on")
>  #endif
> -			"\n",
> -			crc32c_impl());
> +	pr_cont("\n");
>  }
> 
>  static int null_open(struct block_device *bdev, fmode_t mode)

Since we are doing bikeshedding, let me contribute to it :-)

>From scripts/checkpatch.pl:

                if ($line =~ /\bprintk\s*\(\s*KERN_CONT\b|\bpr_cont\s*\(/) {
                        WARN("LOGGING_CONTINUATION",
                             "Avoid logging continuation uses where feasible\n" . $herecurr);
                }

Bart.





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