On Mar 8, 2007, at 3:25 PM, Dieter Baron wrote:

> my goal is to enhance vnd(4) to support UDIF (Apple's Universal Disk
> Image Format; the format .dmg files use).  This format compresses
> chunks (usually 128kb) of the disk, similar to CLOOP2 we already
> support.  It can use zlib or bzip2, and has support for AES-128
> encryption.

Way cool.  I would like to see in-tree tools for creating DMGs, too.   
For reasons that may be obvious to some (:-), I use DMGs a lot, and  
would love to be able to use them on NetBSD.

OS X, FWIW, has a hybrid approach.  Un-encrypted / un-compressed DMGs  
are handled entirely in the kernel-resident driver, IIRC, and stuff is  
only passed to userland if it is necessary to do so.

>
>
>  Should I add support for this inside the kernel, by adding it to
> vnd.c?
>
>  Or is it preferable to have the ability to pass block read/write
> requests to a vnd to a user land process, similar to what puffs does
> for file systems?  That way, we could more easily add support for
> various other image formats, like those used by VMware or qemu.  (As a
> side note, this is how Mac OS X's support for UDIF works.)

I think it would be useful for having a pass-off-to-userland  
interface.  I think with some trickery, you could make it zero-copy,  
too.

-- thorpej