Introduction to the Linux Integration Components


by hjanssen on July 22, 2009 02:02pm

Well, here is blog number two. The initial shock has worn off a bit I hope.

The feedback I have received so far has been pretty positive. This really all started in October of 2008 in a meeting with Mike Neil (GM of Hyper-V) and Tom and myself from the Open Source Technology Center (OSTC) at Microsoft.

In that meeting I proposed to Open Source the Linux Integration Components and contribute them to the Linux Kernel. And, secondly, to have the OSTC continue contributing to these IC's after they made it to the Linux Kernel. Well after some discussion, we all agreed that this was the right thing to do.

And so the whole process started inside of Microsoft.  Hey, what can I say, we like to push the envelope a bit here at the OSTC, and we have a reputation to uphold!

Before I go on, I again wanted to thank the Kernel community (specifically Greg Kroah-Hartman) in helping us with explaining and guiding us through community process. It gave us a very nice jumpstart to get all of this going, and provided the groundwork for a good working relationship with the community. Smile

I have also seen a few patches already submitted by community members, which is excellent! (Moritz Muehlenhoff gets major kudos for the first community contributed patch Big Smile) I will start submitting patches myself next week once the initial submission has stabilized a bit.

It is my plan to use the kernel as my primary development area, and of course I will continue to provide Greg with my patches. My first step is to clean up the code to make sure it fulfills all Kernel coding standards and requirements.

So, here is blog number two: what are the Linux Integration Components?

1.      Overview of Linux VM with ICs

Linux Integration Components(IC) take advantages of the VMBUS and synthetic devices provided in Hyper-V to enhance the performance and usability of Linux guests running on Windows servers.


Figure: Conceptual Architecture overview of Linux guest & Hyper-V. Linux IC modules are painted in yellow color.


VSP: Virtualization Service Provider.

VSC: Virtualization Service Client.

VMBus: Data channel between VSP and VSC.

2.      Linux IC modules -- VMBus and VSCs

  • Communication with parent partition is done through Linux VMBus
  • VSCs are the Linux drivers for synthetic devices (SCSI, IDE, and Ethernet) provided by Hyper-V.
  • They translate between Linux I/O requests and Hyper-V VSC commands
  • Devices are registered with Linux Driver Model (LDM)
  • Every VSC module contains two portions:
  • o Driver Interface Mapper (DIM): Released as open source

This portion of the VSC component interacts with the Linux kernel like a regular Linux device driver.

  • o VSC Core: Released as Open Source

The core portion of the VSC module is implemented based on the protocol of the corresponding VSP at Hyper-V host. The VSC core interacts with VSP via the VMBus interface.

3.      Descriptions for each Linux IC module

3.1 VMBus driver (hv_vmbus.c)

The VMBus driver is a Linux kernel module. It provides both a lightweight bus driver and library functionality. As a bus driver, it registers with Linux Driver Model framework (LDM) to provide simple bus and device integration and device tree integration (sysfs). As a library, it implements the VMBus channel protocol and provide an abstraction of channel to its clients (Disk and Network VSCs).

3.2 StorVSC driver (hv_storvsc.c)

The Storage VSC interacts with the Windows Storage VSP. The "wire" protocol defined by the storage VSP determines how a VSC interacts with it. The Linux Storage VSC (LSVSC) basically abstracts the Linux I/O stack from needing to understand the Storage VSP's protocol. At the upper-edge of the LSVSC, it talks to the Linux SCSI subsystem. The Linux SCSI subsystem sees the LSVSC as a SCSI low-level driver (LLD) in Linux parlance. It passes SCSI requests (scsi_cmnd) to LSVSC which in turn converts them into the "wire" format understood by the Windows Storage VSP (VSTOR_PACKET).  The bottom-edge of the LSVSC talks to Linux VMBus (LVMBUS) which in turn talks to the Windows VMBus to route the packets to the Storage VSP.

3.3 BlkVSC driver (hv_blkvsc.c)

BlkVSC (BlockVSC) supports "fast boot" and fast access to IDE disks. To enable enlightened IDE support for enhancing the performance of Linux when virtualized on Windows, a separate BlockVSC component is used as a Linux block device driver. Like StorVSC, the BlockVSC component is comprised of an upper edge wrapper that interfaces with the Linux block layer and a lower-edge through the infrastructure modules. The infrastructure modules with Hyper-V through the Linux VMBus.

3.4 NetVSC driver (hv_netvsc.c)

The network VSC send and receive network traffic between a Linux guest and Hyper-V host which has direct connection to physical network. The mechanism that this is used to accomplish is the Remote NDIS (RNDIS) protocol. Thus the communication that flows between the VSP and the VSC primarily happens over the RNDIS protocol which then is packaged and forwarded as payload over to the other side over NetVSP / VMBus protocol.

4.      Linux IC's, Location in the Kernel tree

Hopefully you now have a better idea what they are. But where in the kernel tree can you find them?

Well, you can find sources in linux-next tree in /drivers/staging/hv directory.

And the git repository you can find them in right now is:


Or give this command (assuming your system is set up correctly) to download this repository to your machine:

git clone git:// <your local name>

Since the IC's are part of the kernel now, we follow the normal community process of getting this all migrated into Linus mainline kernel.


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