Re: Back to the future.

Pekka J Enberg
2007-04-27T10:12:11Z

Am Freitag, 27. April 2007 08:18 schrieb Pekka J Enberg:
> > No. The snapshot is just that. A snapshot in time. From kernel point of
> > view, it doesn't matter one bit what when you did it or if the state has
> > changed before you resume. It's up to userspace to make sure the user
> > doesn't do real work while the snapshot is being written to disk and
> > machine is shut down.

On Fri, 27 Apr 2007, Oliver Neukum wrote:
> And where is the benefit in that? How is such user space freezing logic
> simpler than having the kernel do the write?
>
> What can you do in user space if all filesystems are r/o that is worth the
> hassle?

I am talking about snapshot_system() here. It's not given that the
filesystems need to be read-only (you can snapshot them too). The benefit
here is that you can do whatever you want with the snapshot (encrypt,
compress, send over the network) and have a clean well-defined interface
in the kernel. In addition, aborting the snapshot is simpler, simply
munmap() the snapshot.

The problem with writing in the kernel is obvious: we need to add new code
to the kernel for compression, encryption, and userspace interaction
(graphical progress bar) that are important for user experience.

Pekka