linux-kernel - Re: [PATCH v2] statx: stx

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Date: Mon, 11 Mar 2024 06:30:21 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Dave Chinner <david@...morbit.com>
Cc: "Darrick J. Wong" <djwong@...nel.org>, Kent Overstreet <kent.overstreet@...ux.dev>, 
	Neal Gompa <neal@...pa.dev>, linux-fsdevel@...r.kernel.org, 
	linux-bcachefs@...r.kernel.org, linux-btrfs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Josef Bacik <josef@...icpanda.com>, 
	Miklos Szeredi <mszeredi@...hat.com>, Christian Brauner <brauner@...nel.org>, 
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH v2] statx: stx_subvol

On Mon, 11 Mar 2024 at 03:17, Dave Chinner <david@...morbit.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