Re: [PATCH 0/3] fanotify support for btrfs sub-volumes

[Christian Brauner <brauner@kernel.org>]

On Mon, Nov 06, 2023 at 04:30:57AM -0800, Christoph Hellwig wrote:
> On Mon, Nov 06, 2023 at 11:59:22AM +0100, Christian Brauner wrote:
> > > > They
> > > > all know that btrfs subvolumes are special. They will need to know that
> > > > btrfs subvolumes are special in the future even if they were vfsmounts.
> > > > They would likely end up with another kind of confusion because suddenly
> > > > vfsmounts have device numbers that aren't associated with the superblock
> > > > that vfsmount belongs to.
> > > 
> > > This looks like you are asking user space programs (especially legacy
> > > ones) to do special handling for btrfs, which I don't believe is the
> > > standard way.
> > 
> > I think spending time engaging this claim isn't worth it. This is just
> > easily falsifiable via a simple grep for btrfs in systemd, lxc, runc,
> > util-linux.
> 
> Myabe you need to get our of your little bubble.  There is plenty of

Unnecessary personal comment, let alone that I'm not in any specific
bubble just because I'm trying to be aware of what is currently going on
in userspace.

> code outside the fast moving Linux Desktop and containers bubbles that
> takes decades to adopt to new file systems, and then it'll take time
> again to find bugs exposed by such odd behavior.

So what?

Whatever you do here: vfsmounts or any other solution will force changes
in userspace on a larger scale and changes to the filesystem itself. If
you accommodate tar then you are fscking over other parts of userspace
which are equally important. There is no free lunch.

Second, we're not going to shy away from changes just because it takes
long for them to be adopted. That's just not a position for us to take.