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

[Nikolay Borisov <nborisov@suse.com>]

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?
> 
> ?
>