Messages in this thread | | | Date | Fri, 27 Apr 2007 13:12:08 +0300 (EEST) | From | Pekka J Enberg <> | Subject | Re: Back to the future. |
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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.
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