linux-kernel - Re: [PATCH] ext4: add a line break for proc mb

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Message-ID: <20160203200706.GG22352@birch.djwong.org>
Date:	Wed, 3 Feb 2016 12:07:06 -0800
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Huaitong Han <huaitong.han@...el.com>, tytso@....edu,
	adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: add a line break for proc mb_groups display

On Wed, Feb 03, 2016 at 11:38:33AM -0800, Joe Perches wrote:
> On Wed, 2016-02-03 at 11:32 -0800, Darrick J. Wong wrote:
> > On Wed, Feb 03, 2016 at 10:30:32AM -0800, Joe Perches wrote:
> > > On Wed, 2016-02-03 at 10:13 -0800, Darrick J. Wong wrote:
> > > > On Wed, Feb 03, 2016 at 09:19:06PM +0800, Huaitong Han wrote:
> > > > > This patch adds a line break for proc mb_groups display.
> > > 
> > > Using 2 lines for output might break any existing users.
> > > 
> > > Are there any?
> > 
> > It's a multiline file if you have more than one blockgroup; this just makes it
> > so that you don't have to special-case BG 0.
> 
> And existing scripts might do that now and might fail
> to do properly after this change.

Or they might have sed -e 's/]#0/]\n#0/g' in which case they won't be affected.

> > IOW: mb_groups scripts already had to parse multiple lines, and most likely any
> > script parsing it would inject a newline after the header.
> 
> I've no dog in this fight really.  I just wanted to make
> it clear that this could cause existing scripts to fail.
> 
> proc output is supposed to be unchanging except maybe
> adding new fields to existing lines.
> 
> Your choice.

Ted's, really.  I have no idea which scripts do with various per-fs /proc
files.  Usually poking in mb_groups is only done as part of failure report data
collection to see what's mucked up the fs this time.

Anyway, I'll defer to the maintainer. :)

--D

> 
> cheers, Joe