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From: Miklos Szeredi <miklos@szeredi.hu>
Date: Mon, 11 Mar 2024 06:30:21 +0100
Message-ID: <CAJfpeguu=DCvtU7dudXNncbxvy5joqS1Xp0Yf590UFPna6qZ2A@mail.gmail.com>
Subject: Re: [PATCH v2] statx: stx_subvol
To: Dave Chinner <david@fromorbit.com>
Cc: "Darrick J. Wong" <djwong@kernel.org>, Kent Overstreet <kent.overstreet@linux.dev>, 
	Neal Gompa <neal@gompa.dev>, linux-fsdevel@vger.kernel.org, 
	linux-bcachefs@vger.kernel.org, linux-btrfs@vger.kernel.org, 
	linux-kernel@vger.kernel.org, Josef Bacik <josef@toxicpanda.com>, 
	Miklos Szeredi <mszeredi@redhat.com>, Christian Brauner <brauner@kernel.org>, 
	David Howells <dhowells@redhat.com>
Content-Type: text/plain; charset="UTF-8"

On Mon, 11 Mar 2024 at 03:17, Dave Chinner <david@fromorbit.com> wrote:
>
> On Fri, Mar 08, 2024 at 08:56:33AM -0800, Darrick J. Wong wrote:
> > Should the XFS data and rt volumes be reported with different stx_vol
> > values?
>
> No, because all the inodes are on the data volume and the same inode
> can have data on the data volume or the rt volume. i.e. "data on rt,
> truncate, clear rt, copy data back into data dev".  It's still the
> same inode, and may have exactly the same data, so why should change
> stx_vol and make it appear to userspace as being a different inode?

Because stx_vol must not be used by userspace to distinguish between
unique inodes.  To determine if two inodes are distinct within a
filesystem (which may have many volumes) it should query the file
handle and compare that.

If we'll have a filesystem that has a different stx_vol but the same
fh, all the better.

Thanks,
Miklos