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Date: Fri, 14 May 2021 13:22:24 -0700
From: Joe Perches <joe@...ches.com>
To: Jason Baron <jbaron@...mai.com>,
Heiner Kallweit <hkallweit1@...il.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86/e820: Use pr_debug to avoid spamming dmesg log
with debug messages
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?
---
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];
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