[GSoC] HAMMER compression and new unionfs

Alex Hornung ahornung at gmail.com
Mon Mar 28 09:01:22 PDT 2011

On 28/03/11 16:48, Naohiro Aota wrote:
> about implementing a new unionfs:
>> The current unionfs is completely broken as it relies on the whiteout
>> VFS technique which is not supported by HAMMER.
> - Then main work would be to implement whiteout feature on HAMMER?
> - or rewrite unionfs code not to depend on whiteout technique?

I've now changed the text on the projects page to reflect that we don't
want a new unionfs using whiteout. So the aim of this project is to
develop a unionfs from scratch avoiding techniques which require messing
with other filesystems.

> and also:
> - Are there some docs (or some source code file) to help me understand
>   DragonFly VFS and HAMMER internal?
> - Are there some detailed guides about these ideas?

About the VFS you can refer to the book "Design & Implementation of
FreeBSD". Things have changed, but it gives a good general perspective
of how things work. The namecache, most interesting part for unionfs,
has no real documentation, only inline with the code.

Alex Hornung

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