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To:     Jason Baron <jbaron@akamai.com>, Joe Perches <joe@perches.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
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From:   Heiner Kallweit <hkallweit1@gmail.com>
Subject: Re: [PATCH 2/2] x86/e820: Use pr_debug to avoid spamming dmesg log
 with debug messages
Message-ID: <6f86e0d5-338e-6321-dacd-8666a30e8f09@gmail.com>
Date:   Fri, 14 May 2021 23:15:16 +0200
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On 14.05.2021 22:32, Jason Baron wrote:
> 
> 
> On 5/14/21 4:22 PM, Joe Perches wrote:
>> On Fri, 2021-05-14 at 15:56 -0400, Jason Baron wrote:
>>>
>>> On 5/14/21 1:38 PM, Joe Perches wrote:
>>>> On Tue, 2021-05-11 at 17:31 -0400, Jason Baron wrote:
>>>>
>>>>> That said, I do see the value in not having to open code the branch stuff, and
>>>>> making pr_debug() consistent with printk which does return a value. So that
>>>>> makes sense to me.
>>>>
>>>> IMO: printk should not return a value.
>>>>
>>>
>>> Ok, the issue we are trying to resolve is to control whether a 'pr_debug()' statement
>>> is enabled and thus use that to control subsequent output. The proposed patch does:
>>>
>>>
>>> +	printed = pr_debug("e820: update [mem %#010Lx-%#010Lx] ", start, end - 1);
>>> +	if (printed > 0) {
>>> +		e820_print_type(old_type);
>>> +		pr_cont(" ==> ");
>>> +		e820_print_type(new_type);
>>> +		pr_cont("\n");
>>> +	}
>>>
>>> I do think pr_debug() here is different from printk() b/c it can be explicitly
>>> toggled.
>>>
>>> I also suggested an alternative, which is possible with the current code which
>>> is to use DYNAMIC_DEBUG_BRANCH().
>>>
>>> if (DYNAMIC_DEBUG_BRANCH(e820_debg)) {
>>>     printk(KERN_DEBUG "e820: update [mem %#010Lx-%#010Lx] ", start, end - 1);
>>>     e820_print_type(old_type);
>>>     pr_cont(" ==> ");
>>>     e820_print_type(new_type);
>>>     pr_cont("\n");
>>> }
>>>
>>> That however does require one to do something like this first:
>>>
>>> DEFINE_DYNAMIC_DEBUG_METADATA(e820_dbg, "e820 verbose mode");
>>>
>>> So I don't feel too strongly either way, but maybe others do?
>>
>> Why not avoid the problem by using temporaries on the stack
>> and not use pr_cont altogether?
> 
> Nice. That's fine with me Heiner?
> 
I once tested a similar approach, just using kasprintf() to dynamically
allocate the substrings. Still using pr_cont() looks a little bit
more elegant to me, but it has its drawbacks. Having said that:
Yes, fine with me (with pr_debug).

> I think though Heiner wants to use pr_debug() below instead of printk
> with KERN_DEBUG, at least that was my understanding. But that would
> be a simpple s/printk/pr_debug().
> 
> Thanks,
> 
> -Jason
> 

Heiner

> 
> 
> 
>> ---
>>  arch/x86/kernel/e820.c | 71 ++++++++++++++++++++++++++++++++------------------
>>  1 file changed, 46 insertions(+), 25 deletions(-)
>>
>> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
>> index bc0657f0deed..a6e7ab4b522b 100644
>> --- a/arch/x86/kernel/e820.c
>> +++ b/arch/x86/kernel/e820.c
>> @@ -184,20 +184,38 @@ void __init e820__range_add(u64 start, u64 size, enum e820_type type)
>>  	__e820__range_add(e820_table, start, size, type);
>>  }
>>  
>> -static void __init e820_print_type(enum e820_type type)
>> +static char * __init e820_fmt_type(enum e820_type type, char *buf, size_t size)
>>  {
>>  	switch (type) {
>> -	case E820_TYPE_RAM:		/* Fall through: */
>> -	case E820_TYPE_RESERVED_KERN:	pr_cont("usable");			break;
>> -	case E820_TYPE_RESERVED:	pr_cont("reserved");			break;
>> -	case E820_TYPE_SOFT_RESERVED:	pr_cont("soft reserved");		break;
>> -	case E820_TYPE_ACPI:		pr_cont("ACPI data");			break;
>> -	case E820_TYPE_NVS:		pr_cont("ACPI NVS");			break;
>> -	case E820_TYPE_UNUSABLE:	pr_cont("unusable");			break;
>> -	case E820_TYPE_PMEM:		/* Fall through: */
>> -	case E820_TYPE_PRAM:		pr_cont("persistent (type %u)", type);	break;
>> -	default:			pr_cont("type %u", type);		break;
>> +	case E820_TYPE_RAM:
>> +	case E820_TYPE_RESERVED_KERN:
>> +		strscpy(buf, "usable", size);
>> +		break;
>> +	case E820_TYPE_RESERVED:
>> +		strscpy(buf, "reserved", size);
>> +		break;
>> +	case E820_TYPE_SOFT_RESERVED:
>> +		strscpy(buf, "soft reserved", size);
>> +		break;
>> +	case E820_TYPE_ACPI:
>> +		strscpy(buf, "ACPI data", size);
>> +		break;
>> +	case E820_TYPE_NVS:
>> +		strscpy(buf, "ACPI NVS", size);
>> +		break;
>> +	case E820_TYPE_UNUSABLE:
>> +		strscpy(buf, "unusable", size);
>> +		break;
>> +	case E820_TYPE_PMEM:
>> +	case E820_TYPE_PRAM:
>> +		scnprintf(buf, size, "persistent (type %u)", type);
>> +		break;
>> +	default:
>> +		scnprintf(buf, size, "type %u", type);
>> +		break;
>>  	}
>> +
>> +	return buf;
>>  }
>>  
>>  void __init e820__print_table(char *who)
>> @@ -205,13 +223,14 @@ void __init e820__print_table(char *who)
>>  	int i;
>>  
>>  	for (i = 0; i < e820_table->nr_entries; i++) {
>> -		pr_info("%s: [mem %#018Lx-%#018Lx] ",
>> +		char type[32];
>> +
>> +		pr_info("%s: [mem %#018Lx-%#018Lx] %s\n",
>>  			who,
>>  			e820_table->entries[i].addr,
>> -			e820_table->entries[i].addr + e820_table->entries[i].size - 1);
>> -
>> -		e820_print_type(e820_table->entries[i].type);
>> -		pr_cont("\n");
>> +			e820_table->entries[i].addr + e820_table->entries[i].size - 1,
>> +			e820_fmt_type(e820_table->entries[i].type,
>> +				      type, sizeof(type)));
>>  	}
>>  }
>>  
>> @@ -465,6 +484,8 @@ __e820__range_update(struct e820_table *table, u64 start, u64 size, enum e820_ty
>>  	u64 end;
>>  	unsigned int i;
>>  	u64 real_updated_size = 0;
>> +	char type1[32];
>> +	char type2[32];
>>  
>>  	BUG_ON(old_type == new_type);
>>  
>> @@ -472,11 +493,10 @@ __e820__range_update(struct e820_table *table, u64 start, u64 size, enum e820_ty
>>  		size = ULLONG_MAX - start;
>>  
>>  	end = start + size;
>> -	printk(KERN_DEBUG "e820: update [mem %#010Lx-%#010Lx] ", start, end - 1);
>> -	e820_print_type(old_type);
>> -	pr_cont(" ==> ");
>> -	e820_print_type(new_type);
>> -	pr_cont("\n");
>> +	printk(KERN_DEBUG "e820: update [mem %#010Lx-%#010Lx] %s ==> %s\n",
>> +	       start, end - 1,
>> +	       e820_fmt_type(old_type, type1, sizeof(type1)),
>> +	       e820_fmt_type(new_type, type2, sizeof(type2)));
>>  
>>  	for (i = 0; i < table->nr_entries; i++) {
>>  		struct e820_entry *entry = &table->entries[i];
>> @@ -543,15 +563,16 @@ u64 __init e820__range_remove(u64 start, u64 size, enum e820_type old_type, bool
>>  	int i;
>>  	u64 end;
>>  	u64 real_removed_size = 0;
>> +	char type[32];
>>  
>>  	if (size > (ULLONG_MAX - start))
>>  		size = ULLONG_MAX - start;
>>  
>>  	end = start + size;
>> -	printk(KERN_DEBUG "e820: remove [mem %#010Lx-%#010Lx] ", start, end - 1);
>> -	if (check_type)
>> -		e820_print_type(old_type);
>> -	pr_cont("\n");
>> +	printk(KERN_DEBUG "e820: remove [mem %#010Lx-%#010Lx]%s%s\n",
>> +	       start, end - 1,
>> +	       check_type ? " " : "",
>> +	       check_type ? e820_fmt_type(old_type, type, sizeof(type)) : "");
>>  
>>  	for (i = 0; i < e820_table->nr_entries; i++) {
>>  		struct e820_entry *entry = &e820_table->entries[i];
>>
>>