On Fri, Feb 4, 2011 at 2:20 AM, Joel Becker [off-list ref] wrote:

On Fri, Feb 04, 2011 at 12:33:39AM +0200, Amir Goldstein wrote:

quoted

I have been working on porting Next3 snapshots to Ext4
with a group of 4 CS students.

This is where it all happens:
https://github.com/amir73il/ext4-snapshots

Ext4 snapshots prototype is already working!
Would you like to see a demo?

I would like to present the progress of our work
and discuss the remaining issues and how they should be best addressed.

Additionally, I would like to discuss the need for a unified snapshots API that
would serve both Ext4 and Btrfs.
This could be useful for someone that wants to implement a generic
snapshots management system.

       ocfs2 definitely wants to be a part of that discussion, as we
already do snapshots and thin clones.  ocfs2 snapshots are actually just
thin clones marked readonly.  They can be placed anywhere in the
filesystem and are first-class inodes.  They do not live in a hidden
space like Next3 snapshots seem to.
       I've already got a design for a front-end snapshot program that
implements a policy on top this generic behavior.  This design would
cover both first-class and hidden style snapshots, because it assume
snapshots are in a distinct namespace.  I haven't gotten around to
implementing it yet, but btrfs and other snapshottable filesystems were
part of the design goal.

Joel

Hi Joel,

Any chance of getting a copy of that design of yours, to get a head start
for LSF?

Here are some other generic snapshot related topics we may want to discuss:

1. Collaborating the use of inode flags COW_FL, NOCOW_FL, suggested by Chris.
2. How to deal with mmap write to COW file, when you get ENOSPC.
3. Adding buffer_remap() flag for buffered I/O code, meaning, there is
an existing mapping to initialize a page on partial write, but still need
to call get_block() to get a (possibly) new mapping.

I'll be staying for Collaboration summit, so I've got plenty of time
if you like to exchange some ideas.

Amir.
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html