Zack's Kernel News

Microsoft GPLs Hyper-V Drivers

Microsoft has released their Hyper-V drivers under the GPL, Greg Kroah-Hartman announced recently. He praised Microsoft's Hank Janssen, Haiyang Zhang, and Sam Ramji, and a bunch of non-Microsoft folks, for making the whole thing happen. The patches essentially help Linux run well as a guest on top of a Hyper-V virtualized system.

Some folks, such as Dave Jones, wanted to review the patches, but found they needed so much cleanup that it was difficult to make sense of them. Others agreed, and Greg explained that first the known, working patches were going into the tree as they were, so that if any of the cleanups broke their workingness, it would be easy to track down the problem later. Once the drivers and the cleanups were in place, he said, everyone would be able to review the cleaned-up code without pain.

Balbir Singh asked how the drivers would remain synced up with Microsoft's version. How would updates be incorporated into the kernel? Greg replied that the long-term plan was for the in-kernel version to be the primary version. He said Microsoft would abdicate developmental control and remove the drivers from their own website. Hank from Microsoft also chimed in, saying, "It is my plan to use the kernel as my primary development area, and I will continue to provide Greg with updates. First step is to clean up the code to make sure it fulfills all kernel coding standards and requirements. Then I will start contributing new functionality."

Obstacles Still Facing PramFS

Marco Stornelli has submitted PramFS for inclusion in the mainline kernel. This was previously attempted in 2004 by MontaVista, and the effort failed in part because of patent issues surrounding the code. PramFS supports non-volatile RAM that can keep state across reboots and power-cycles, essentially turning that RAM into a hard disk available to the user.

According to Marco and to Daniel Walker, MontaVista has abandoned pursuit of a patent on the PramFS code, thus clearing the way for inclusion in the kernel.

The discussion immediately turned to technical considerations. Was the filesystem robust enough? Was there sufficient justification for a new filesystem as opposed to just using an existing one like ext2? Would it support standard filesystem features like hard links? In the midst of this, it was clear that Pavel Machek violently opposed PramFS, saying there wasn't sufficient justification for using it instead of something like ext2 or ext3, or even just modifying the RAMdisk code to handle persistence across reboots.

Ultimately, Marco was unable to convince Pavel of the value of PramFS, although Pavel did express interest in the fact that one of Marco's tests showed PramFS is significantly faster than ext2. This probably won't be enough to turn the debate around, however. It does seem as though PramFS might have to implement hard links, journaling, and other features before it is considered for inclusion.

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