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Date: Thu, 9 Nov 2023 06:41:21 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
	Josef Bacik <josef@toxicpanda.com>,
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	Chris Mason <clm@fb.com>, David Sterba <dsterba@suse.com>,
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Subject: Re: [PATCH 0/3] fanotify support for btrfs sub-volumes
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On Thu, Nov 09, 2023 at 10:07:35AM +0100, Christian Brauner wrote:
> > How?  If they want to only rely on Posix and not just he historical
> > unix/linux behavior they need to compare st_dev for the inode and it's
> > parent to see if it the Posix concept of a mount point (not to be
> > confused with the Linux concept of a mountpoint apparently) because
> > that allows the file system to use a new inode number namespace.
> 
> That doesn't work anymore. Both overlayfs and btrfs make this
> impossible or at least inconsistent.

One you hit a different st_dev on btrfs you'll stay on that until
you hit a mount point or another (nested) subvolume.  Can't comment
on overlayfs.  But if it keeps mixing things forth and back what would
the semantics of the flag be anyway?