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Projection FileSystem Build Status

ProjFS is a FUSE filesystem aiming at providing a general way of doing filesystem projection: project directories and files to a new mount point by converting specified files through a custom projection command.

It can provide use cases such as automatically converting audio files while keeping the original file.


This project is written in Rust, so just follow the standard way how a Rust application is built:

cargo build


Basic usage

projfs <source> <mountpoint>

The <mountpoint> is where the new projected filesystem hierarchy will appear. It is (apparently) read-only.

By default, the program performs the projection by using ffmpeg to convert every audio and video file to ogg file (audio) (unless it's ogg audio already).

It identifies files by MIME type (using the mime_guess crate). All files are provided as-is except for audio/* and video/* files which are going to be projected. The command used to convert is ffmpeg -i <original_file> -vn <output_file>. File suffix is changed to ogg where applicable.

Advanced usage

Please see the help document using:

projfs --help

An example projection specification is available in example_projection.yml. It also corresponds to the default behaviour. See the next section for a detailed explanation of the projection specification.

Projection Configuration

An example projection configuration file is placed under example_projection.yml, which is the same as not specifying a projection configuration file. The detail of the schema is explained here.

The configuration-schema.owl file is an ontology describing the schema (i.e. the same as below). RDF/OWL may be promoted to one of the acceptable configuration file types in the future.

The configuration uses YAML format. The acceptable keys are specified below. Every key is mandatory unless marked as [optional].

  • mime_types: a list of strings File matching mime types specified here will be converted using the projection_command, unless it's specified in ignored_mime_types. Each string is either a mime type (e.g. audio/ogg), or a wildcard of mime types (e.g. audio/*). Specifically, shorthand of wildcard (e.g. audio, or audio/) is accepted, but not encouraged.
  • ignored_mime_types: [optional] a list of strings The mime types specified here will not be converted. The acceptable values are the same as mime_type.
  • name_mapping: a string The string is the new suffix which the converted file will have. It will replace the original file suffix if any (e.g. file1.wav -> file1.ogg if ogg is specified here).
  • projection_command: a string The string specifies the command used to do the conversion. It can accept two varirables, {input} and {output}: Each will be replaced with the corresponding source file path ({input}) and output (cache) file path ({output}). The string will be separated by space and passed to Command module. That means there should not be escaped spaces (i.e. \ ), quoted spaced (e.g. " qwe"), etc. Were there any needs to use them, you can write your own script and point to it from here.


  • Having a default cache dir
  • Copying file attributes from source file (except for size)
  • Different cache dirs for different source dirs
  • Update cache only when necessary
  • Return placeholder information for files under-projection
  • Accept configuration
    • Custom filetype
    • Custom projection command
    • A list of configurations
  • One-to-many projection
  • Background automatic async cache
  • Update cache while running
  • Validate configuration before loading


Except for certain files specified afterwards, this project is licensed under the Apache 2.0 License as stated below.

Copyright notice

Copyright 2019 renyuneyun (Rui Zhao)

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


The following files under the source directory (src/) are directly obtained from the fuse-mt project (commit), licensed under Apache 2.0 license and MIT license:

  • libc_bridge/
  • libc_bridge/

The and libc_bridge/ files contain unmodified code from fuse-mt.


Projection FileSystem is a FUSE filesystem performs directory content projection








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