linux-kernel - Re: Printk mulitple line message support

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Date:	Tue, 15 Nov 2011 08:50:01 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Joe Perches <joe@...ches.com>
Cc:	William Douglas <william.r.douglas@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Printk mulitple line message support

On Mon, 2011-11-14 at 22:40 +0800, Joe Perches wrote:
> On Mon, 2011-11-14 at 14:58 +0800, Huang Ying wrote:
> > Hi,
> > 
> > In most cases, printk only guarantees messages from different printk
> > calling will not be interleaved between each other.  But many printk
> > users uses multiple line to form a complete message and call printk
> > for each line.  So the following situation is possible for two printk
> > users running on two CPUs.
> > 
> > line 1 of message from printk user1
> > line 1 of message from printk user2
> > line 2 of message from printk user1
> > line 2 of message from printk user2
> > 
> > This makes kernel log hard to read.  One possible solution to this
> > issue is to give a sequence number (or ID) to each complete message.
> > So the above lines will be:
> > 
> > {1}line 1 of message from printk user1
> > {2}line 1 of message from printk user2
> > {1}line 2 of message from printk user1
> > {2}line 2 of message from printk user2
> > 
> > Then some simple script can be used to group lines together according
> > to sequence number in lines.
> > 
> > What do you think about that?
> 
> This makes the typical multi-part but non-interleaved
> output difficult to read.

With a simple script, we can strip out the sequence # easily.

> How about determining if there is interleaving and
> emitting sequence # only in those cases?
> 
> Perhaps test the atomic for the last sequence #.

So we will have no sequence # prefix for printk user1's lines if printk
user 2 comes in the middle?  Something as follow?

line 1 of message from printk user1
{2}line 1 of message from printk user2
line 2 of message from printk user1
{2}line 2 of message from printk user2

This will make it hard for a script to sort the lines.  Where should it
insert lines from printk user2 in the sort result?

Best Regards,
Huang Ying


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