linux-kernel - RE: [RFC PATCH 1/5] printk: implement pr_cont

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Date:   Thu, 20 Aug 2020 07:44:23 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Joe Perches' <joe@...ches.com>,
        John Ogness <john.ogness@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH 1/5] printk: implement pr_cont_t

From: Joe Perches
> Sent: 20 August 2020 01:34
> 
> On Thu, 2020-08-20 at 01:32 +0206, John Ogness wrote:
> > Implement a new buffering mechanism for pr_cont messages.
> >
> > Old mechanism syntax:
> >
> >     printk(KERN_INFO "text");
> >     printk(KERN_CONT " continued");
> >     printk(KERN_CONT "\n");
> >
> > New mechanism syntax:
> >
> >     pr_cont_t c;
> >
> >     pr_cont_begin(&c, KERN_INFO "text");
> 
> bikeshed:
> 
> I suggest:
> 
> 	printk_begin(&printk_context, fmt, ...)
> 	printk_continue(&printk_context, fmt, ...) (maybe printk_next())
> 	printk_end(&printk_context, fmt, ...)

I see some very long source lines looming ...

Blue bikeshed:

You'd probably want printk_end(&ctx, NULL) to work.
Although the example doesn't show where the '\n' comes from.
Although I guess it is now inferred and actually deleted
from 'normal' printk() call.

I've no idea how you'd 'size' the number of buffers.
You could use kmalloc(), perhaps falling back on a local buffer.
While might lead to:
	pr_init(&ctx, level, GFP_KERNEL);
	pr_cont(&ctx, fmt, ...);
	pr_flush(&ctx);

	David

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