Editing Filesystem in Userspace (section)

== Operation and usage ==
[[File:FUSE structure.svg|thumb|right|280px|A flow-chart diagram showing how FUSE works: Request from userspace to list files (ls -l /tmp/fuse) gets redirected by the Kernel through VFS to FUSE. FUSE then executes the registered handler program (./hello) and passes it the request (ls -l /tmp/fuse). The handler program returns a response back to FUSE which is then redirected to the userspace program that originally made the request.]]
To implement a new file system, a handler program linked to the supplied <code>libfuse</code> library needs to be written. The main purpose of this program is to specify how the file system is to respond to read/write/stat requests. The program is also used to [[Mount (computing)|mount]] the new file system. At the time the file system is mounted, the handler is registered with the kernel. If a user now issues read/write/stat requests for this newly mounted file system, the kernel forwards these IO-requests to the handler and then sends the handler's response back to the user.

[[File:Unmount SSHFS.png|thumb|right|Unmounting a FUSE-based file system with the <code>fusermount</code> command]]

FUSE is particularly useful for writing [[virtual file system]]s. Unlike traditional file systems that essentially work with data on mass storage, virtual filesystems don't actually store data themselves. They act as a view or translation of an existing file system or storage device.

In principle, any resource available to a FUSE implementation can be exported as a file system.