[GSoC] HAMMER compression and new unionfs

[Naohiro Aota]

Matthew Dillon <dillon at apollo.backplane.com> writes:

> :src/sys/sys/namecache.h or sys/kern/vfs_cache.c?  These are guesses on my
> :part, cause I'm not familiar with it.  Matt did a lot of work on the
> :namecache back in 2003/2004; I linked to some of it on the Digest:
> :
> :http://www.shiningsilence.com/dbsdlog/index.php?s=namecache
> :
> :Material there may lead you to more information, I hope.
>
>     The unionfs code hasn't worked in years, and I don't think any of
>     it is salvageable.  Also, the original unionfs code (and probably
>     FreeBSD's current code too) depends on whiteouts which HAMMER does
>     not support.  They never worked very well even in FreeBSD.
>
>     A new unionfs would require a complete rewrite from scratch and a
>     new approach to recording file deletions.

hm, seems difficult for me.. To have "whiteout database file" on the top
of writable directory, would be another implementation? Then how can I
avoid reading from/writing to the database file?

Regards,
Naohiro