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[[!toc levels=2]]

# Filesystems in userspace: puffs, refuse, FUSE, and more

## About

NetBSD now offers full support for running file systems in userspace.  Major
components are "puffs", which is the kernel subsystem that realizes the
pass-to-userspace framework file system, as well as the userland libraries that
support constructing file system implementations. These are libpuffs and the
FUSE compatibility library, librefuse.

This page describes the situation in NetBSD 5.0 and later.

## Components

There are a number of components interacting to provide routines for userland
file systems: puffs as the kernel part, and libpuffs and librefuse to provide
functions for userland file systems to call. The following image gives an
overview of the components and their connections:

![Overview about puffs](/puffs/puffs.png)  
**Overview about puffs**

The components themselves are:

 * **puffs** is the core component inside the kernel. It exposes a file system
   interface towards the userland programs (accessible via `/dev/puffs` and
   libpuffs), and communicates with the kernel's own idea of files, which are
   represented as vnodes. The puffs kernel component and how to interface it is
   described further in the MAN.PUFFS.4 manpage.

 * The **libpuffs** library is the interface between userland file systems
   and the kernel component. It provides a number of convenience routines that
   userland file systems can use, and is described in the MAN.PUFFS.3 manpage.

 * To facilitate running the huge amount of file systems already available for
   the FUSE interface, but not dictate the capabilities of puffs by it, it was
   decided that FUSE support should be provided as a compatibility layer on top
   of the native puffs interface, which is offered by **librefuse**. The
   re-implementation of the FUSE functionality is designed to be source code
   compatible with FUSE, and it is further described in the

Examples for puffs and refuse filesystems can be found in the the NetBSD source
tree in `src/share/examples/{puffs,refuse}`.

## Enabling puffs

puffs is enabled by default in GENERIC on major architectures starting from
NetBSD 5.0. For a custom kernel, the following are required in the kernel

    file-system     PUFFS
    pseudo-device   putter

Alternatively, modules can be used.

## Base system examples

This section presents usage examples for file systems shipped with the NetBSD
base system.

### psshfs, The NetBSD sshfs

See the manpage for

    # mount_psshfs /puffs
    # ls /puffs
    AdobeFnt.lst    OS                  bin     public_html
    Desktop         OpenOffice.org1.1.0 in      tmp
    # cd /puffs
    # ls -l .cshrc
    -rw-r--r--  1 39068  2000  4706 Jun 16 01:01 .cshrc
    # head -2 .cshrc
    # Default .cshrc for Solaris, Irix, ...
    # md5 .cshrc
    MD5 (.cshrc) = 2ad1d2606a5678f312709a388376c2e5
    # ls -l test
    ls: test: No such file or directory
    # date >test
    # ls -l test
    -rw-r--r--  1 39068  2000  29 Nov 23 01:19 test
    # cat test
    Thu Nov 23 01:19:36 MET 2006
    # umount /puffs

### 9P file servers

See the [Bell manpage]( and
the [NetBSD manpage 9p(8)](

    # mount_9p nobody@ /puffs
    # cd /puffs
    # echo 9puffs in action > msg_from_earth
    # ls -l msg_from_earth
    -rw-r--r--  1 nobody  wheel  17 Apr 25 23:24 msg_from_earth
    # rsh cat /tmp/msg_from_earth
    9puffs in action

Since there is currently no support in the implementation for access control or
support for authentication, the account nobody was picked just to prove a point.
The NFS nobody user really does not have anything to do with 9P. Support for
access control and use of pre-established secure connections will be added to
`mount_9p` on a later date.

## pkgsrc & FUSE

FUSE compatibility was added within pkgsrc, and besides the required
infrastructure work a number of FUSE packages were added to pkgsrc in the new
*filesystem* category. Example packages that are currently available include:

 * [fuse](
   -- filesystem in userspace (compat headers, pkg-config files, etc.), needed for
   pkgsrc on Linux

 * [fuse-archivemount](
   -- FUSE gateway to libarchive

 * [fuse-cddfs](
   -- FUSE filesystem that uses libparanoia for audio CDs

 * [fuse-ntfs-3g](
   -- a NTFS driver with read and write support

 * ...

More packages are currently being worked on, please see
for a full list.

Here is an example of installing and using the FUSE-enabled NTFS-3g

    # cd pkgsrc/filesystems/fuse-ntfs-3g
    # make install
    # ntfs-3g ntfs.img /ntfs

Using FUSE file systems on NetBSD 4.0 is possible, but in addition to adding
puffs support support to the kernel, it requires fetching and manually
installing a backport of the ReFUSE library. The library is available
and further instructions are available

## Further Information

An in-depth technical description of puffs was presented at 
[AsiaBSDCon]( 2007 in a paper entitled
*puffs - Pass-to-Userspace Framework File System*. The
[paper]( and
[slides]( are available.

The ReFUSE emulation layer for FUSE file systems is described in
*[ReFUSE: Userspace FUSE Reimplementation Using puffs](/puffs/refuse.pdf)*
presented at EuroBSDCon 2007.

A [paper]( discussing the 
implementation of distributed file systems on top of puffs was presented at 
AsiaBSDCon 2008.

The [puffs(3)]( manual pages provide further 
information from a development perspective.

The source code in browsable form:

 * [kernel code](
 * [libpuffs](
 * [librefuse](
 * [puffs file systems in the base system](
 * [source code examples of other puffs file systems](
 * [source code examples for refuse](

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