LUFS: ex ftpfs, sshfs, etc
Reading time: 2 – 4 minutes
is enabling you to mount into your file hierarchy a remote computer’s file
system, which is accessible by various means (ftp, ssh, etc.). Then, the access
to the remote files will be completely network transparent. In other words,
you’ll be able to read/modify remote files as if they were local, watch
movies/listen to MP3s from FTP/SSH/Gnutella servers without copying them
locally.
The reason for the
userspace stuff: there are operations only suited for userspace
(cryptography for example) and implementing them in kernel would be
bloat.
The reason for the kernel
stuff: I think it’s important to keep the file system access point at
the lowest level in order to allow all the applications to use it.
Consider KDE: it implements its own virtual file system, a great one,
but only KDE applications can take advantage of it. So does GNOME, MC
and others. Suddenly we have lots of overlapping userspace file
system implementations, a real waste…
Communication between the
kernel module and the daemon is done through UNIX domain sockets.
This makes LUFS best suited for networked file systems, where this
indirection overhead (userspace <-> kernel <-> userspace)
is small compared to the speed penalty due to the network itself.
LUFS can be regarded as
doing the same job as the VFS (virtual file system switch) in the
kernel: it is a switch, distributing the file system calls to its
supported file systems. With a big difference: LUFS file systems are
implemented in userspace. This would be a drawback for local file
systems where the access speed is important, but proves to be a huge
advantage for networked file systems where the userland
flexibility is most important.
This flexibility allowed
for implementation of SSHFS for example, in a pretty straightforward
manner, using the already existing openssh
infrastructure. Lots of other exotic file systems are in the
planning phase: socketfs, httpfs, webdavfs, freenetfs, etc. Just
imagine mounting a freenet file system and accessing all the goodies
as they were local…