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Microsoft owns the patent to the Virtual File Allocation Table (VFAT) filesystem variant that allows long as well as short (8.3) filenames. Earlier this year, the Redmond company and TomTom had come to a legal agreement about its use in TomTom's navigation software. To avoid further patent issues, Samba developer Tridgell sent a first patch to the kernel list in May that disabled long filenames in VFAT. Many developers objected because the patch restricted Linux functionality to FAT.

Tridgell's followup patch takes a clever approach and a better chance at a speedy acceptance in the kernel. An option now exists to disable VFAT_FS_DUALNAMES to avoid creating both 8.3 and long filenames, the essential patent issue. Instead, it creates either one or the other but not both, with 8.3 filenames now including invalid characters by Microsoft standards, the clever workaround to make them unidentifiable as FAT files.

A caveat to this solution is a regression in the patch that older non-VFAT DOS systems with Linux long filenames can no longer read these files -- not an issue for most users. Tridgell does, however, warn that enabling the option could have VFAT dual-filename "implications."

How long Microsoft's FAT patents continue to hold is yet undetermined. The Open Invention Network has been steadily looking for prior art evidence from the community to invalidate the patents. In the meantime, Tridgell's patch should provide some security against any further claims.

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