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Date: Wed, 7 Feb 2024 15:26:55 -0500
From: Kent Overstreet <kent.overstreet@linux.dev>
To: Theodore Ts'o <tytso@mit.edu>
Cc: brauner@kernel.org, linux-fsdevel@vger.kernel.org, 
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/7] filesystem visibililty ioctls
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References: <20240206201858.952303-1-kent.overstreet@linux.dev>
 <20240207174009.GF119530@mit.edu>
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On Wed, Feb 07, 2024 at 12:40:09PM -0500, Theodore Ts'o wrote:
> On Tue, Feb 06, 2024 at 03:18:48PM -0500, Kent Overstreet wrote:
> > previous:
> > https://lore.kernel.org/linux-fsdevel/20240206-aufwuchs-atomkraftgegner-dc53ce1e435f@brauner/T/
> > 
> > Changes since v1:
> >  - super_set_uuid() helper, per Dave
> > 
> >  - nix FS_IOC_SETUUID - Al raised this and I'm in 100% agreement,
> >    changing a UUID on an existing filesystem is a rare operation that
> >    should only be done when the filesystem is offline; we'd need to
> >    audit/fix a bunch of stuff if we wanted to support this
> 
> NAK.  First, this happens every single time a VM in the cloud starts
> up, so it happens ZILLIONS of time a day.  Secondly, there is already
> userspace programs --- to wit, tune2fs --- that uses this ioctl, so
> nixing FS_IOC_SETUUID will break userspace programs.

You've still got the ext4 version, we're not taking that away. But I
don't think other filesystems will want to deal with the hassle of
changing UUIDs at runtime, since that's effectively used for API access
via sysfs and debugfs.