[BitTorrent] Re: bt2 protocol features

Stephen Thomas flabdablet at yahoo.com
Thu Jun 10 21:45:27 EDT 2004


--- In BitTorrent at yahoogroups.com, Olaf van der Spek <OvdSpek at L...>
wrote:
> So if you edited for example a configuration file, it's name would 
> change and you'd have to edit the symlink to link to the new name?
> That doesn't sound very nice to me.

This would indeed not be a terribly convenient file system to do
*everything* with; its strength would be in storing archival content.

However, let's look at one possibly way the filesystem could handle
that configuration file change.

At a given access point - perhaps per local machine - you'd need a
local filesystem root.  At any time, that would just be a certain hash
value.

When you edit your configuration file, the filesystem would add new
leaf nodes.  As it did so, it would create new internal nodes to point
to those leaves; this effect would propagate until you had a new hash
tree root for that file.

If non-leaf nodes include data lengths as well as hash values, this
can be done without disrupting large numbers of existing nodes; only
those in the direct path from the replaced leaves to the root need
change.

At some convenient time - probably on file close - the filesystem
would work its way backward through the pathname toward the local
filesystem root, modifying directory files as it went (these
modifications would happen the same way as they did on the original
file).

You'd end up with new hashes for the modified config file and for all
the directory files back to the local filesystem root.  Depending on
policy, you could either discard the old ones or keep them around for
backup.

There would actually be no need for symlinks.  The only thing symlinks
give you over hard links is the ability to cross file system
boundaries; with hash values working like universal i-node numbers,
there are no boundaries that need crossing.

Efficient garbage collection would be an issue.




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