From the title, I thought Microsoft had sponsored an improvement in generic FreeBSD.<p>From the revision, it seems the improvement is in a Hyper-V storage driver.
I mean, this only makes sense -- OSes are no longer a core product in the server world; they're just a part of the application stack. The hypervisor / orchestrator is the critical part, and that's Hyper-V in the Microsoft world.<p>Also, this patch doesn't strike me as monumental. Really, it strikes me as one of the first things you would do when configuring a disk driver for a VM (mapped I/O is unnecessary overhead for most VM configurations as the hypervisor and/or SAN remaps it anyway). Has Microsoft not supported FreeBSD well under HyperV in the past?
I don't understand mapped vs unmapped io in terms of Hyper-V. Does that mean that io from a user process goes directly to a paravirtualized io device and bypasses the freebsd kernel?
The style of this diff is bewildering. What's with the gratuitous reformatting of the whitespace? Makes it difficult for the reader to pick out the meaningful difference.