Re: [PATCH 2/2] x86/e820: Use pr_debug to avoid spamming dmesg log with debug messages
From: Jason Baron
Date: Fri May 14 2021 - 16:32:26 EST
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 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
> ---
> 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];
>
>