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Date: Wed, 10 Dec 2025 17:54:38 +0100
From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, cem@kernel.org,
	linux-xfs@vger.kernel.org
Subject: Re: [PATCH] xfs: validate that zoned RT devices are zone aligned
Message-ID: <20251210165438.GA9489@lst.de>
References: <20251210142305.3660710-1-hch@lst.de> <20251210164859.GB7725@frogsfrogsfrogs>
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On Wed, Dec 10, 2025 at 08:48:59AM -0800, Darrick J. Wong wrote:
> mkfs doesn't enforce that when you're creating a zoned filesystem on
> non-zoned storage:
...
> (The mkfs enforcement does work if you have an actual zoned storage
> device since mkfs complains about changes in the zone sizes.)

Ugg, and I thought only my horrible hacks caused that..

> 
> > to avoid getting into trouble due to fuzzers or mkfs bugs.
> >
> > Fixes: 2167eaabe2fa ("xfs: define the zoned on-disk format")
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> How many filesystems are there in the wild with rump rtgroups?

I suspect very, very few as zoned mode on non-zoned devices is not a
widely advertised feature, and then you'd also need wiredly sized device
or manual override to get it.  And then scrub would complain about it.

> Given that runt zoned rtgroups can exist in the wild, how hard would it
> be to fix zonegc?

Very nasty.  We can't ever GC into one.