Re: [PATCH v2 5/5] mkfs.xfs: add configuration file parsing support using our own parser

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, May 17, 2018 at 10:24:13PM -0500, Eric Sandeen wrote:
> On 5/17/18 2:27 PM, Luis R. Rodriguez wrote:
> > You may want to stick to specific set of configuration options when
> > creating filesystems with mkfs.xfs -- sometimes due to pure technical
> > reasons, but some other times to ensure systems remain compatible as
> > new features are introduced with older kernels, or if you always want
> > to take advantage of some new feature which would otherwise typically
> > be disruptive.
> > 
> > This adds support for parsing a configuration file to override defaults
> > parameters to be used for mkfs.xfs.
> > 
> > We define an XFS configuration directory,/etc/mkfs.xfs.d/  and allow for
> > different configuration files, if none is specified we look for the
> > default configuration file, /etc/mkfs.xfs.d/default. You can override
> > with -c.  For instance, if you specify:
> > 
> > 	mkfs.xfs -c experimental -f /dev/loop0
> > 
> > The file /etc/mkfs.xfs.d/experimental will be used as your configuration
> > file. If you really need to override the full path of the configuration
> > file you may use the MKFS_XFS_CONFIG environment variable.
> 
> I'm swamped under a deadline at work this week so just commenting at a
> very high level for now, but I'm curious; why use an env var vs
> providing a full path for -c ?  env vars always strike me as magic unexpected
> behaviors.
> 
> # mkfs.xfs -c /my/fancy/path/to/config
> 
> seems much clearer than
> 
> # export MKFS_XFS_CONFIG=/my/fancy/path/to/
> # mkfs.xfs -c config
> 
> i.e. if a full path is specified use it, else use the config directory.
> 
> Thoughts?

In this case your choices are:
MKFS_XFS_CONFIG=/my/fancy/path/to/config mkfs.xfs

or:
cp /my/fancy/path/to/config /etc/mkfs.xfs.d/hoogah
mkfs.xfs -c hooga

<shrug> Bikeshedding more, what if either option accepted either an
absolute path, or a file in $sysconfdir/etc/mkfs.xfs.d/ ?  And the -c
option can be specified once to override the environment variable /
builtin detaults?

--D

> 
> Thanks,
> -Eric
> 
> > To verify what configuration file is used on a system use the typical:
> > 
> >    mkfs.xfs -N
> > 
> > There is only a subset of options allowed to be set on the configuration
> > file, and currently only 1 or 0 are acceptable values. The default
> > parameters you can override on a configuration file and their current
> > built-in default settings are:
> > 
> > [data]
> > noalign=0
> > 
> > [inode]
> > align=1
> > projid32bit=1
> > sparse=0
> > 
> > [log]
> > lazy-count=1
> > 
> > [metadata]
> > crc=1
> > finobt=1
> > rmapbt=0
> > reflink=0
> > 
> > [naming]
> > ftype=1
> > 
> > [rtdev]
> > noalign=0
> > 
> > Signed-off-by: Luis R. Rodriguez<mcgrof@kernel.org>
> --
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