Re: [PATCH] BTRFS-PROG: recursively subvolume snapshot and delete

[David Sterba <dsterba@suse.cz>]

On Thu, Nov 28, 2013 at 08:23:13PM +0100, Goffredo Baroncelli wrote:
> Definetely you are right. In fact this is true also for other tools like
> tar: they complaint if you remove/move/rename a file during the copy. We
> can work to increase the robustness of the process, to avoid strange
> behaviour when a subvolume is removed/moved/renamed.
> 
> Anyway I am more afraid that we can't mix recursive and readonly snapshot.

Agreed, this would eg. need to toggle RO/RW status when needed, but this
does not sound very clean.

> Implementing the atomic recursive snapshot in the kernel, is out of my
> possibility; anyway basically this means that the filesystem is frozen
> until all the snapshot are done, which requires a finite time. In case
> of a high number of subvolumes this could be a problem.

High number of subvolumes to snapshot atomically will always be
problematic and a lazy userspace-based recursive snapshot might be
actually better regarding the impact on the rest of the system, but
without guaranteed atomicity.

But, I don't want to kill the whole idea just because there's some
scenario that's possible but hard to handle.

david