linux-kernel - Re: [PATCH v6 02/11] printk: Use struct console for suppression and extended console state

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Message-ID: <84plmw527r.fsf@jogness.linutronix.de>
Date: Fri, 15 Nov 2024 09:36:00 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Chris Down <chris@...isdown.name>, Petr Mladek <pmladek@...e.com>
Cc: linux-kernel@...r.kernel.org, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Sergey Senozhatsky
 <senozhatsky@...omium.org>, Steven Rostedt <rostedt@...dmis.org>, Geert
 Uytterhoeven <geert@...ux-m68k.org>, Tony Lindgren
 <tony.lindgren@...ux.intel.com>, kernel-team@...com
Subject: Re: [PATCH v6 02/11] printk: Use struct console for suppression and
 extended console state

On 2024-10-28, Chris Down <chris@...isdown.name> wrote:
> In preparation for supporting per-console loglevels, modify
> printk_get_next_message() to accept the console itself instead of
> individual arguments that mimic its fields.

Sorry, this is not allowed. printk_get_next_message() was created
specifically to locklessly retrieve and format arbitrary records. It
must never be tied to a console because it has nothing to do with
consoles (as can bee seen with the devkmsg_read() hack you added in the
function).

I recommend adding an extra argument specifying the level.

The extra argument would be redundant if may_suppress=false. So perhaps
as an alternative change "bool may_suppress" to "u32 supress_level". The
loglevels are only 3 bits. So you could easily define a special value
NO_SUPPRESS to represent the may_suppress=false case.

#define NO_SUPPRESS BIT(31)

bool printk_get_next_message(struct printk_message *pmsg, u64 seq,
                             bool is_extended, u32 suppress_level);

Then in devkmsg_read():

printk_get_next_message(&pmsg, atomic64_read(&user->seq), true, NO_SUPRRESS)

John Ogness