Subject: Re: compressed vnd, cgd and encryption
To: Daniel Carosone <>
From: Nathan J. Williams <>
List: tech-kern
Date: 06/26/2006 10:04:40
Daniel Carosone <> writes:

> and finally I get what you were concerned about: will this work
> directly with vnd on the cgd device raw, without a filesystem in
> between?  no. vnd will need a filesystem to hold the file, cgd or not.

This has always seemed like a bug or weakness in the "vndcompress"
implementation. vnd(4) provides a file-to-device mapping; having the
decompression support in there means that we only support
compressed-file-to-device. In contrast, if the decompression layer
were a separate device-to-device mapping (zd?), we could support both
modes (file->vnd->zd->filesystem and (xxxd->zd->filesystem). This would
also be good for, say, images in flash in an embedded system, where
you want to drop the image into some address block of flash, but
there's not much value in a "wrapper" filesystem.

        - Nathan