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Date: Wed, 8 Nov 2023 00:12:36 -0800
From: Christoph Hellwig <hch@infradead.org>
To: Christian Brauner <brauner@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>,
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Subject: Re: [PATCH 0/3] fanotify support for btrfs sub-volumes
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On Wed, Nov 08, 2023 at 09:09:10AM +0100, Christian Brauner wrote:
> > a bind mount can of course change the dev_t - if it points to a
> > different super block at the moment.
> 
> No, a bind mount just takes an existing directory tree of an existing
> filesystem and makes it visible on some location in the filesystem
> hierarchy. It doesn't change the device number it will inherit it from
> the superblock it belongs.

That's what I'm trying to say.

So if you have:

	/mnt/1/ with dev 8
	/mnt/2/ with dev 23

then a bind mount of

	/mnt/1/foo to /mnt/2/bar will get your dev 8 for /mnt/2/bar

So the device number changes at the mount point here, bind mount or not.