Userfs is a system I wrote in 1993 or so to allow user processes to be mounted as a normal filesystem.  It worked reasonably well, and the most common use was ftpfs, which allowed anonymous FTP with a filesystem interface. The code I wrote was basically a proof-of-concept prototype, and therefore riddled with problems.

I abandoned it in 1996 or so, with the intent of rewriting it using the lessons learned from the userfs experience.  Unfortunately I haven't had time to do so, so userfs is orphaned.  Noone has taken up the "official maintainer" role, but there have been a number of people hacking it since.

The code has aged.  The last release I made will only work with 1.3/2.0 kernels, and does not compile against glibc.  Fixing the glibc issues are relatively simple, but it would be a fair amount of work to make it work with 2.1/2.2 kernels.

A post-mortem

So, what were the lessons?

Good things:

Bad things: Part of the problem was that when I originally started writing it, userfs was intended to be a prototyping testbed for filesystems which would eventually end up in the kernel, which is why it exposed as close to the raw VFS interface as possible.  As time went on, most of the interesting filesystems were ones which would never go in the kernel, and the VFS-like interface became a serious liablility.  Future userfs-like filesystems should definitely go with a more abstract filesystem interface.


Here's an incomplete list of userfs resources:

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Comments? Questions? Mail me.  Last updated:  4 November 2002