linux-ext4 - Re: [PATCH 8/9] mke2fs: Add orphan

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Message-ID: <20210805150013.GM14483@quack2.suse.cz>
Date:   Thu, 5 Aug 2021 17:00:13 +0200
From:   Jan Kara <jack@...e.cz>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH 8/9] mke2fs: Add orphan_file feature into mke2fs.conf

On Wed 04-08-21 15:04:10, Theodore Ts'o wrote:
> On Mon, Jul 12, 2021 at 05:43:14PM +0200, Jan Kara wrote:
> > Enable orphan_file feature by default in larger filesystems. Since the
> > feature is COMPAT, older kernels will just ignore it and happily work
> > with the filesystem as well.
> > 
> > Signed-off-by: Jan Kara <jack@...e.cz>
> 
> We'll need to decide whether we want to enable this by default, at
> least initially.  The general practice has been to not enable new
> kernel functionality right away by default.  It's true that older
> kernels will ignore the feature if they aren't orphan_file aware;
> however, we if have a file system which is created with orphan_file
> eanbled, but that file system with the orphan_file feature is made
> available to a system which is running an orphan_file-aware kernel,
> but the distro hadn't picked up the a version e2fsprogs which is
> orphan_file-aware.  This might happen if the file system was created
> on one system, and then it gets connected to an system w/o a new
> version of e2fsprogs (e.g. via fibre channel, iscsi, AWS EBS, GCE PD,
> etc), then could be a surprise to the user.  So that's something for
> us to discuss.

Yes, I think you are right that enabling the functionality by default right
from the start may be too aggressive. I'm fine with postponing this for
some time.

> In the shorter term, there's another problem I've notied, which is if
> we add this to mke2fs.conf, and the user runs:
> 
> 	mke2fs -t ext4 -O ^has_journal foo.img 1G
> 
> mke2fs will fail mid-way through the mkfs process with the error
> message, "mke2fs: cannot set orphan_file flag without a journal".
> This represents a regression, and if we don't want to drop orphan_file
> from the default feature set in mke2fs.conf, I think we'll need to
> check for the case where the file system doesn't have a journal, and
> only fail when the user has explicitly requested orphan_file on the
> command line.  But if orphan_file is a default as defined in
> mke2fs.conf, and the journal is not present for whatever reaseon, we
> need to silently disable the orphan_file feature.

Good catch. I'll fix this.

> (Also note that to avoid user confusion, we should refer to
> orphan_file as a "feature" instead of a "flag".  Even for things like
> "orphan_present" or "recovery_needed" it is probably clearer to call
> them features, simply because it makes it easier for system
> adminsitrators and developers to be able to find the "flag" location.)

Good point. I've fixed up couple of occurences of 'flag' I've found in the
messages.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR