[uml-devel] Humfs metadata api tdb backend

[uml-devel] Humfs metadata api tdb backend

[Piotr Neuman]

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I've been working on metadata backend that would use tdb (meta_tdb). It's 
advantages over meta_fs include:

- proper handling of "metadata" named files and dirs,
- compactness (no directory/files structure overhead and storing data in 
binary),

Performace is yet to be tested extensively and compared to meta_fs.

There are also additions to humfs features:

- humfs stores file/dir access modes now (fixes some chmod problems),
- humfs automatically initializes mount dir if only valid "superblock" file is 
present in it (no other files, new humfsify is not yet ready ;),

Example "superblock" is attached. To try meta_fs backend with it just change 
"tdb" to "shadow_fs". To mount humfs:

mount none <uml mount dir> -t humfs -o <host dir>

The patch is against UML release ver. 2.4.26-1. This release is of beta 
quality (should mostly work ;), but please note:

- database format is subject to change (right now db keys may collide, though 
it is very unlikely, I coded new fixed structure but it's not fully debugged 
yet),
- meta_tdb does not support unmouting and remounting (since metadata unmount() 
method is not called by humfs, this is no issue for meta_fs becose of the way 
it operates).

The patch is also available here:

http://kem.p.lodz.pl/~peter/humfs-2.4.26-1-meta_tdb-1.patch.bz2

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version 1
used 394962944
total 734003200
metadata tdb

[uml-devel] Humfs metadata api tdb backend

[Piotr Neuman]

One more thing: access mode support makes meta_fs backend incomaptible with 
the vanilla 2.6.26-1 one and Jeff Dike's humfsify.


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[uml-devel] Humfs metadata api tdb backend

[Piotr Neuman]

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This version should be pretty close to final. I hope Jeff Dike will include it 
in the next 2.4 UML release.

Changes:
- tdb keys are now safe not to ever collide,
- Humfs now supports unmounting (that makes meta_tdb fully operational),
- fixed some bugs.

Simple program to list metadata from tdb file is included (tdbfsck).

Metadata structure kept in tdb may still change in an uncompatible way.

Patch also available at:
http://kem.p.lodz.pl/~peter/humfs-2.4.26-1-meta_tdb-2.patch.bz2

ps. Thanks to Oleg Drokin for reviewing my code.

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version 1
used 394962944
total 734003200
metadata tdb