Microsoft patents: Linux to become VFAT-free?

In light of the recent Microsoft-TomTom VFAT lawsuit and its subsequent settlement, Linux users have been wondering what Microsoft's intentions with regard to the presence of VFAT functionality in the Linux kernel might be.

The Linux Foundation continues to maintain that Microsoft's VFAT patents are not valid. And of course the United States is one of only a small handful of countries that even recognise software patents.

However, according to CNet, the Linux community has recently been taking steps to work around the entire VFAT patent issue. But what is the nature of the VFAT patents, and how can Linux bypass them?

The historical point of VFAT

MS-DOS and older versions of Windows (versions prior to 95) could only read filenames in the short 8.3 format. VFAT was designed to accommodate the use of older software programs written for MS-DOS and pre-95 versions of Windows by allowing any given file to have a long filename (technically up to 256 characters) and a short 8.3 one. Newer programs would see the long version and display that to users. Older programs would see the short version.

This kludge was not perfect. If a user created a DOC file named, say, "Letter to the Prime Minister.DOC" in Word 95 or higher, the VFAT functionality would automatically and invisibly create and store a short version of the name (here, it might be something like "LETTE~01.DOC") so that older software that could only recognise the 8.3 format would be able to see and open the file. However, if that file were then opened in, say, Word 6.0 (as "LETTE~01.DOC"), edited and then saved again, the long version of the filename would be lost.

Imperfect as this functionality may have been, it did allow for a more or less smooth transition to long filenames. Nowadays, however, almost no one has a need for this functionality. Yet it is built into the standard FAT/FAT32 file format used on almost every USB and flash device out there.

Because Microsoft claims patents regarding this VFAT functionality, it was able to sue TomTom and extract from that company concessions in an out-of-court settlement. Linux users more generally--and particularly corporate Linux users--have since worried that Microsoft may be wanting to sue them for the simple reason that, while Linux does not contain Microsoft code (and so does not violate any copyrights), it does contain the VFAT functionality (and so could be taken as stepping on Microsoft's patent).

Fixing the problem

The TomTom case has had Linux coders working to alter the way Linux works to avoid any potential claims by Microsoft. The current favourite, now being vetted by Linux patent lawyers and considered for inclusion in the kernel, involves filling the short version of a given file name with dummy data, rendering useless the VFAT functionality claimed in the patents.

The key to the patents involves allowing a long filename to be seen and edited and saved by software that can only see its short version. The Linux fix keeps the framework of long and short filenames intact, but breaks that functionality--effectively, you can use the long filename without any problem, but the short filename would become unreadable by older software programs that demanded it.

This loss of functionality, however, would not matter to the vast majority of people out there, as almost no one these days uses pre-Windows 95 operating systems.

Whither VFAT?

At the end of the day, Microsoft may never seek to attack Linux directly over its VFAT patents. Those patents, as noted, only apply in the United States and a small number of other countries. They do not apply, for instance, in the EU and most of Asia.

Besides, its VFAT patents were already once ruled invalid in the United States. Although Microsoft was later able to get them reinstated, it is unlikely they would want to risk a second invalidation.

Finally, the use of the FAT/FAT32 format with VFAT functionality in billions of devices across the world actually limits Microsoft's ability to act on their patents. If they seek to enforce those patents more broadly, they may find themselves in more trouble for abusing their monopoly.