Re: [PATCH 3/3] ovl: redirect on rename-dir

From: Miklos Szeredi
Date: Mon Nov 07 2016 - 03:08:22 EST

On Sun, Nov 6, 2016 at 8:14 PM, Konstantin Khlebnikov <koct9i@xxxxxxxxx> wrote:
> On Wed, Oct 26, 2016 at 2:12 PM, Miklos Szeredi <miklos@xxxxxxxxxx> wrote:
>> On Tue, Oct 25, 2016 at 1:57 PM, Raphael Hertzog <hertzog@xxxxxxxxxx> wrote:
>>> Do you plan to make it the default in the future when it has been
>>> available for a while?
>>> Barring any regression introduced by your patch, it seems that the feature
>>> is best available by default since it allows legitimate operations to
>>> succeed that are otherwise refused. I understand that it makes it
>>> impossible to mount the overlay filesystem with an older kernel but is
>>> that problem more widespread than the one we're fixing here? On my side,
>>> overlayfs is only used in scenarios where the kernel is always the same
>>> (or newer compared to what created the initial filesystem).
>> I think it would be safe to make it the default if upperdir is empty.
>> Nonempty implies that it was created with old kernel (or it was
>> crafted by hand). But there should be a way to explicitly turn it
>> off; either because of the need for backward compatibility or because
>> the old format is simply easier to work with for humans.
>> How about:
>> - If upper is nonempty, then leave redirect feature alone except when
>> mount option "-oredirect=on" is used to force enabling it.
>> - If upper is empty, then enable redirect feature except when mount
>> option "-oredirect=off" is used to force disabling it.
> I don't like this empty-nonempty upper logic.
> I think this feature should be off by default and be enabled
> explicitly in mount option.
> Available features could be listed in sysfs /sys/fs/overlay/..., like ext4 does.
> Overlayfs mounting anyway is complicated operation.
> User must know a lot about it and provide persistent state for each mount:
> list layers in correct order, work and uppder directory on the same disk, etc.
> Enabled features is a part of this state.
> Probably this could be solved in userspace tool "mount.overlay" - it could load
> features and layers from config file or xattr and set required mount
> options automatically.

It seems there are some conflicting opinions here. I have mine too,
but I'll let this simmer and concentrate on actual features for now.