Request For Comment: VDI Binary Image Specification

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Request For Comment: VDI Binary Image Specification

Postby PainterEnterprises » 8. Apr 2009, 22:17

I've been through the available open source repository, lots of Google search results, FAQs and manuals and I've found not one bit of data related to the actual binary image format of the VDI.

As an example: I can download the binary-image spec for Microsoft's VHD file format, which enables me to create a small program to open and edit VHD Header and Footer data so I can (for example) straight copy a 25GB VHD file into a new folder, slap a fresh UUID on the copy VHD file in about a nanosecond, and then have the original and the copy loaded into VirtualBox simultaneously. Using a similar method, I can expand fixed-sized VHD files at will by simply dropping a new empty file of the desired size onto my hard drive and then passing through the existing file bit-by-bit to make a mirror-image, then rewrite the header and footer to the appropriate value data so Virtual PC and VirtualBox can use them as if they were native, at which point I just have to start up the virtual machine and expand the primary partition (or create a new partition in the extra space).

What I'd really very much appreciate is a VDI specification document I can use to do the same thing with this format.

Thanks,

Andrew
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Re: Request For Comment: VDI Binary Image Specification

Postby TerryE » 9. Apr 2009, 00:50

The VirtualBox dev team doesn't publish a spec, but then again it does publish the source code and an API to the disk handling utilities that's documented in the SDK. Swings and roundabouts. Also see my tutorial All about VDIs, if you want to understand the internals.
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Re: Request For Comment: VDI Binary Image Specification

Postby PainterEnterprises » 9. Apr 2009, 00:52

That is exactly what I'm looking for!

Thanks very much, Terry. For the pointer and the documentation in the first place :-)

Edit:

I guess it bears mentioning that the search feature on the board index as well as on the 'Using VirtualBox' board, using terms like "VDI" and "VDI SPEC" and "VDI SPECIFICATION" did not turn up that tutorial at all.

If I'd been more inclined to actually read the board instead of just search for what I wanted, I see how that I would have found it right there in the stickies at the top, but it looks a little like the regex in the search feature is borked.
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Re: Request For Comment: VDI Binary Image Specification

Postby vbox4me2 » 9. Apr 2009, 11:32

For searching google is your friend "search keywords site:forums.virtualbox.org"
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Re: Request For Comment: VDI Binary Image Specification

Postby TerryE » 9. Apr 2009, 14:57

PainterEnterprises wrote:I guess it bears mentioning that the search feature on the board index as well as on the 'Using VirtualBox' board, using terms like "VDI" and "VDI SPEC" and "VDI SPECIFICATION" did not turn up that tutorial at all.

We are gently encouraging the VBox team to host a community Wiki where we can keep this sort of stuff, but this sort of thing comes down to the time available and priorities amongst the dev team and community supporters that are involved. I would say that there's a 50:50 change that we will have a starting wiki up in the next month or so.
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Re: Request For Comment: VDI Binary Image Specification

Postby PainterEnterprises » 21. Jul 2009, 22:30

Hello again.

I had pulled TerryE's tutorial some time back, but I'm only just getting the chance to start looking over it. The tutorial is great, but I need a lot more information.

For example:

It'd be really nice to know what actual name has been assigned to each data field in the Header structure just so I don't have to refer to 'the field located at offset X in the VDI Header.'

I also absolutely need explicit definitions for each field usage. What exactly is an Image Signature field used for and is it totally unique to a VDI image like a short UUID, or is it some kind of checksum? If it is a checksum, how is the value calculated? What are the various possible values for the Image Type field and what does each value represent? What are the various possible values for the Image Flags field, and is this a byte or bit field, and what would each value represent? How are Cylinders, Sectors, and Heads calculated and are they required or optional (can they all be zeroed out unless the drive is some specific type)?

I've done some more searching (both in this Forum and as per prior suggestions from this forum, via Google) in hopes of finding the answers to these questions, but it seems like even the OSE version doesn't have this kind of technical application detail available. I'm smart enough to know that the guys working on the OSE aren't working in the dark, but I'm not smart enough to figure out how to turn on the flashlight. Can anybody point me in the right direction?

Thanks,

Andrew
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Re: Request For Comment: VDI Binary Image Specification

Postby TerryE » 22. Jul 2009, 15:07

Like many FLOSS products, the source code is really the only true specification. Google VirtualBox svn. The Storage components are in src/VBox/Devices/Storage, and the modules which implement the VDI functionality are VDICore.h and VDIHDDCore.cpp. Even if you can't program comfortably in C++, it is still quite readable and understandable if you have any knowledge of programming.
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Re: Request For Comment: VDI Binary Image Specification

Postby PainterEnterprises » 22. Jul 2009, 17:03

Thanks for the illumination (again), Terry. Looks like everything I need is in there, including full coder comments! (Who would have guessed, right? Never occurred to me to go dig up the source when I knew I couldn't read it anyway)
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Re: Request For Comment: VDI Binary Image Specification

Postby TerryE » 22. Jul 2009, 19:49

Reading C++ if you've done any programming is pretty straight forward, though the for (i=0;i<n;i++) loop syntax throws people at first. But it's still quite easy to get the gist of what is going on. Writing it is entirely a different matter and the main problem is learning all the bloody libraries. Still, it gets quite easy after you've learnt your first dozen languages :lol:
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Re: Request For Comment: VDI Binary Image Specification

Postby IsoBuster » 25. May 2016, 20:39

TerryE wrote:Also see my tutorial [...]All about VDIs, if you want to understand the internals.


Great, based on this tutorial I was able to implement *.vdi support in my software in less than a day !
Easy straightforward format, thanks !
Peter, IsoBuster Guy,
Regards
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