linux-kernel - Re: [RFC PATCH 0/1] ovl: brtfs' temp_fsid doesn't work with ovl index=on

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Message-ID: <aPB7VOaDhBtZTD6T@infradead.org>
Date: Wed, 15 Oct 2025 21:57:56 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Amir Goldstein <amir73il@...il.com>
Cc: André Almeida <andrealmeid@...lia.com>,
	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
	linux-unionfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kernel-dev@...lia.com, Miklos Szeredi <miklos@...redi.hu>,
	Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
	Anand Jain <anand.jain@...cle.com>,
	"Guilherme G . Piccoli" <gpiccoli@...lia.com>
Subject: Re: [RFC PATCH 0/1] ovl: brtfs' temp_fsid doesn't work with ovl
 index=on

On Wed, Oct 15, 2025 at 01:09:26PM +0200, Amir Goldstein wrote:
> FWIW this operation already exists in export_operations.
> It is currently only used by pnfs and only implemented by xfs.
> I would nor object for overlayfs to use this method if implemented
> and fall back to copying uuid directly from s_uuid

The get_uuid export operation is specifically about an on-disk superblock
that the pnfs client can match.  Overloading it for in-core information
would be very confusing and also problematic if it doesn't exist on-disk
in this format.  In retrospective it should be called get_disk_uuid or
something similar.