linux-kernel - Re: [PATCH 2/4] printk: store instead of processing cont parts

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Message-ID: <87ft9kx6er.fsf@jogness.linutronix.de>
Date:   Tue, 21 Jul 2020 17:03:16 +0206
From:   John Ogness <john.ogness@...utronix.de>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kexec@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] printk: store instead of processing cont parts

On 2020-07-21, Sergey Senozhatsky <sergey.senozhatsky@...il.com> wrote:
>> That said, we have traditionally used not just "current process", but
>> also "last irq-level" as the context information, so I do think it
>> would be good to continue to do that.
>
> OK, so basically, extending printk_caller_id() so that for IRQ/NMI
> we will have more info than just "0x80000000 + raw_smp_processor_id()".

If bit31 is set, the upper 8 bits could specify what the lower 24 bits
represent. That would give some freedom for the future.

For example:

0x80 = cpu id (generic context)
0x81 = interrupt number
0x82 = cpu id (nmi context)

Or maybe ascii should be used instead?

0x80 | '\0' = cpu id (generic context)
0x80 | 'i'  = interrupt number
0x80 | 'n'  = cpu id (nmi context)

Just an idea.

John Ogness