News

Microsoft Submits Its exFAT Code to Linux

• By Kurt Mackie
• 08/30/2019

Microsoft this week cleared its Extended File Allocation Table (exFAT) technology to be added to the Linux kernel.

According to this Aug. 28 Linux kernel maintainers post, the exFAT code was submitted for "staging" on the Linux kernel, although it's said to still need "a lot of work." The timing and availability of exFAT in the Linux kernel will be up to the Linux kernel maintainers, a Microsoft spokesperson clarified via e-mail.

Microsoft's exFAT technology, introduced in 2006, is code that serves as a file system for handling files larger than 4GB. It's typically used in portable storage devices, such USB drives and Secure Digital memory cards.

Microsoft has licensed its exFAT technology to companies such as Samsung and Paragon Software, which offer their own exFAT versions. Other companies also use exFAT technology in their products. Microsoft's exFAT patents have served as a kind of wealth-extraction vehicle over the last few years, and the Linux community especially resented Microsoft's practices in that respect.

GPLv2 Support
The exFAT code addition to the Linux kernel will support the creation of "conformant interoperable implementations," Microsoft's announcement explained.

Microsoft also supports "the eventual inclusion of a Linux kernel with exFAT support in a future revision of the Open Invention Network's Linux System Definition, where, once accepted, the code will benefit from the defensive patent commitments of OIN's 3,040+ members and licensees."

Possibly, that statement means that in the near future, Microsoft won't sue OIN members that use Linux for infringing exFAT patents. The OIN is a patent nonaggression organization that uses a pool of patents defensively against Linux patent infringement claims against its members. Microsoft joined the OIN as a member late last year.

However, joining the OIN wasn't a sufficient assurance. in the opinion of the Software Freedom Conservancy, a nonprofit group advocating for free and open source software. The group had asked Microsoft, when it joined the OIN, "to upstream the exFAT code under GPLv2-or-later to confirm its intention to end patent aggression," according to an Aug. 30 blog post.

It turns out that Microsoft does intend to specify exFAT code as part of the open source GNU General Public License (GPL) version 2, according to the spokesperson.

"The technical specification for exFAT is freely available to all, and exFAT code incorporated into the Linux kernel will be available under GPLv2," the spokesperson indicated.

The Software Freedom Conservancy added that the steps to add exFAT to Linux won't be wholly complete until "Microsoft distributes a copy of Linux themselves that contains this technology." Microsoft needs to distribute its own Linux copy with exFAT because the OIN's patent license "is not as comprehensive as a full patent license from Microsoft," the group explained.

"Eventually, Microsoft will likely distribute a version of Linux containing exFAT to its Azure users and in its Windows Subsystem for Linux," the conservancy added. "However, until that occurs, the issue is not really resolved."

Industry Timing
In recent years, Microsoft has played nice with Linux, and even favored developing its own software first for Linux in some cases. The switch with regard to exFAT, though, is all due timing and industry needs, according to the spokesperson:

When we first developed exFAT many years ago, it was technology that held a lot of promise, but was not widely used. Over time, file sizes have grown, and users' needs have changed, making the use cases for exFAT more broad based. exFAT has also become an industry standard via the SD Card Association.

Partners that build their own exFAT versions also will be able to take advantage of the Linux kernel addition.

"We will continue to support our commercial partners who develop and market exFAT implementations of their own," the spokesperson stated. "If they prefer, they can take advantage of exFAT in Linux."

Meanwhile, Paragon Software this week announced Linux kernel 5.2 support for its proprietary "Microsoft exFAT by Paragon" driver, which is covered by Microsoft patent rights. Paragon claims to support the "highest data throughput speeds possible" with its solution, which can be used on Android, Linux, Mac OS X and Windows systems.