[GSoC] HAMMER compression and new unionfs

Naohiro Aota naota at elisp.net
Mon Mar 28 17:24:14 PDT 2011

Alex Hornung <ahornung at gmail.com> writes:

> 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.

I see. I'd like to know what features to be implemented on the "new
unionfs". Are there any working or developing example on other BSDs or
on Linux? I mean the "new unionfs" would have features like FreeBSD
unionfs or Linux aufs2 [1], or much different thing?

>> 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.

Thanks! I'll check the book and the code.

[1] http://aufs.sourceforge.net/


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