Re: [PATCH 0/9] mkfs.xfs: add mkfs.xfs.conf support

From: Eric Sandeen <sandeen@sandeen.net>
To: "Luis R. Rodriguez" <mcgrof@kernel.org>
Cc: Jan Tulak <jtulak@redhat.com>, Dave Chinner <david@fromorbit.com>,
	linux-xfs@vger.kernel.org, jack@suse.com,
	Jeff Mahoney <jeffm@suse.com>,
	okurz@suse.com, Libor Pechacek <lpechacek@suse.com>
Subject: Re: [PATCH 0/9] mkfs.xfs: add mkfs.xfs.conf support
Date: Thu, 11 May 2017 17:57:51 -0500	[thread overview]
Message-ID: <646aa740-a9fc-98df-df9f-6b89bbed7261@sandeen.net> (raw)
In-Reply-To: <20170511224603.GA28800@wotan.suse.de>

On 5/11/17 5:46 PM, Luis R. Rodriguez wrote:

> FWIW, I've looked at ways to address this without your future work Jan, ie
> backporting this feature, and ultimately have decided to *not* allow any
> command line overwrite for options specified in the configuration file. So
> for the backported versions of this feature a user will only be able to
> overwrite if the config file is commented out or removed.
> 
> How we end up doing this upstream may differ given we may have a way to
> properly do sanity checks overall and treat "defaults" as real "defaults".
> But without such mechanisms implementing a sensible way to overwrite things
> in a compatible way was just crap.
> 
> As such for the backported versions of this feature I'll make this big note
> on the man page:

I'm a little confused - backported from where to where?  I'm not sure what
a "backport" means in this context, when there is no upstream solution at this
time.

> """
> One  of  the uses of the configuration file is to enable distributions
> to provide mkfs.xfs(8) updates from a base distribution release and enable to
> create filesystems which are sure to remain supported and compatible. As such
> systems with a mkfs.xfs.conf(5) file present have very likely been well thought
> out, and  overriding configuration  file  defaults is discouraged unless you
> know what you are doing and are familiar with the associated risks.  If you
> know what you are doing, wish to waive compatibility, and wish to overwrite the
> configuration file provided the best option is to either remove or uncomment
> the  configuration  file  completely  as options cannot be overwritten on the
> command line.
> """

So are you planning a forked, non-upstream behavior for your distro?

I think that disallowing commandline overrides of configfile settings is a
mistake, and not what we'd want upstream.  If you do it as a fork, mkfs should
fail if conflicting options are specified, IMHO.  The worst of all possible
worlds is an admin typing an otherwise valid mkfs command, and getting a
"successful" result which is /not/ what was specified by the user.

Honestly, until an upstream solution is found, simply patching in new defaults
seems safest (and least-element-of-surprise) for a distro.

Thanks,
-Eric