linux-kernel - [RFC] Make dynamic debug infrastructure more flexible

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Date:   Thu, 21 May 2020 13:06:10 -0700
From:   Joe Perches <joe@...ches.com>
To:     Jason Baron <jbaron@...mai.com>
Cc:     Vikash Garodia <vgarodia@...eaurora.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [RFC] Make dynamic debug infrastructure more flexible

On Thu, 2020-05-21 at 09:08 -0700, Joe Perches wrote:
> On Thu, 2020-05-21 at 16:28 +0300, Stanimir Varbanov wrote:
> > Here we introduce few debug macros with levels (low, medium and
> > high) and debug macro for firmware. Enabling the particular level
> > will be done by dynamic debug.
> 
> I'd rather make the logging level facility generic in
> dynamic debug than prefix all formats with what could
> be non-specific content.
> 
> From a long time ago:
> 
> https://groups.google.com/forum/#!msg/linux.kernel/VlWbno-ZAFw/k_fFadhNHXcJ

Hey Jason.

I believe there are 6 bits left in the unsigned int
use for the line number and flags in struct _ddebug

Assuming the use of a mechanism like

	pr_debug_level(level, fmt, ...)

would you be OK with something like this to enable a
level or bitmask test of dynamic debug logging output?

where the output is controlled by something like

echo 'file <filename> level <n> +p' > <debugfs>/dynamic_debug/control

to enable dynamic debug output only at level <n> or higher
or maybe match a bitmap of <n>

(modulo all the rest of the code necessary to use it?)
---
 include/linux/dynamic_debug.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index abcd5fde30eb..616dbb2b5921 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -38,6 +38,8 @@ struct _ddebug {
 #define _DPRINTK_FLAGS_DEFAULT 0
 #endif
 	unsigned int flags:8;
+	unsigned int level:5;
+	unsigned int level_is_bitmask:1;
 #ifdef CONFIG_JUMP_LABEL
 	union {
 		struct static_key_true dd_key_true;