Re: option to mount read-only subvolume with read-write access

[Eric Levy <contact@ericlevy.name>]

> So that would be a silent change in the subvolume and not detectable 
> by
> eg. checking the generation. That would break incremental send at 
> least
> and goes against the point of read-only subvolume.

> Yeah but the other mount points would see the old data, depending on 
> the
> cached status of the blocks.

Perhaps a different feature would be needed, then, of a new property 
that makes a subvolume appear as read-only, at least from the 
standpoint of the VFS, when accessed through a mount point higher on 
the file tree, but not when mounted directly.

>> I think it does not have a well defined semantics, what you ask 
>> seems to
> be some kind of multi headed subvolume that could appear different
> depending on the way it's accessed from the VFS mount point which is 
> out
> of reach in many cases.

I'm not sure whether this means the same as I just wrote, or not.

> I'd probably need to understand what you mean in the first sentence 
> "At
> times it is helpful", I don't have an idea where it would be helpful.

In some scenarios, upcoming changes to a file tree, intended to become 
the default mounts in future boot sessions, will be staged in a closed 
environment, which may include use of "chroot". It is helpful for the 
subvolume to be read-write in the environment created by temporary 
mount points, but still protected from accidental modification through 
its physical location on the root tree.