In
computer science, a synthetic file system or a pseudo file system is a hierarchical interface to non-file objects that appear as if they were regular files in the tree of a disk-based or long-term-storage
file system. These non-file objects may be accessed with the same
system calls or
utility programs as regular files and
directories. The common term for both regular files and the non-file objects is ''node''.
The benefit of synthetic file systems is that well-known file system semantics can be reused for a universal and easily implementable approach to
interprocess communication. Clients can use such a file system to perform simple file operations on its nodes and do not have to implement complex
message encoding and passing methods and other aspects of
protocol engineering Protocol engineering is the application of systematic methods to the development of communication protocols. It uses many of the principles of software engineering, but it is specific to the development of distributed systems.
History
When the f ...
. For most operations, common file utilities can be used, so even
scripting is quite easy.
This is commonly known as
everything is a file
Everything is a file is an idea that Unix, and its derivatives handle input/output to and from resources such as documents, hard-drives, modems, keyboards, printers and even some inter-process and network communications as simple streams of bytes ...
and is generally regarded to have originated from
Unix.
Examples
/proc filesystem
In the Unix-world, there is commonly a special filesystem
mount
Mount is often used as part of the name of specific mountains, e.g. Mount Everest.
Mount or Mounts may also refer to:
Places
* Mount, Cornwall, a village in Warleggan parish, England
* Mount, Perranzabuloe, a hamlet in Perranzabuloe parish, ...
ed at
/proc
The proc filesystem (procfs) is a special filesystem in Unix-like operating systems that presents information about processes and other system information in a hierarchical file-like structure, providing a more convenient and standardized meth ...
. This filesystem is implemented within the
kernel
Kernel may refer to:
Computing
* Kernel (operating system), the central component of most operating systems
* Kernel (image processing), a matrix used for image convolution
* Compute kernel, in GPGPU programming
* Kernel method, in machine learni ...
and publishes information about
processes. For each process, there is a directory (named by the
process ID
In computing, the process identifier (a.k.a. process ID or PID) is a number used by most operating system kernels—such as those of Unix, macOS and Windows—to uniquely identify an active process. This number may be used as a parameter in variou ...
), containing detailed information about the process:
status
Status (Latin plural: ''statūs''), is a state, condition, or situation, and may refer to:
* Status (law)
** City status
** Legal status, in law
** Political status, in international law
** Small entity status, in patent law
** Status confere ...
, open files,
memory maps, mounts, etc.
/proc first appeared in Unix 8th Edition, and its functionality was greatly expanded in
Plan 9 from Bell Labs.
Linux /sys filesystem
The /sys filesystem on Linux complements /proc, by providing a lot of (non-process related) detailed information about the in-kernel status to userspace. More traditional Unix systems locate this information in sysctl calls.
ObexFS
ObexFS is a
FUSE
Fuse or FUSE may refer to:
Devices
* Fuse (electrical), a device used in electrical systems to protect against excessive current
** Fuse (automotive), a class of fuses for vehicles
* Fuse (hydraulic), a device used in hydraulic systems to protect ...
-based filesystem that provides access to
OBEX objects via a filesystem. Applications can work on remote objects via the OBEX protocol as if they were simply (local) files.
Plan 9 file servers
On the
Plan 9 from Bell Labs operating system family, the concept of
9P synthetic filesystem is used as a generic
IPC method. Contrary to most other operating systems, Plan 9's design is heavily distributed: while in other OS worlds, there are many (and often large) libraries and frameworks for common things, Plan 9 encapsulates them into fileservers. The most important benefit is that applications can be much simpler and that services run network and platform agnostic - they can reside on virtually any host and platform in the network, and virtually any kind of network, as long the fileserver can be mounted by the application.
Plan 9 drives this concept expansively: most operating system services, e.g. hardware access and networking stack are presented as fileservers. This way it is trivial to use these resources remotely (e.g. one host directly accessing another host's block devices or network interfaces) without the need of additional protocols.
Other implementations of the 9P file system protocol also exists for many other systems and environments.
Embedded systems
Debugging embedded systems or even system-on-chip (SoC) devices is widely known to be difficult.
Several protocols have been implemented to provide direct access to in-chip devices, but they tend to be proprietary, complex and hard to handle.
Based on
9P, Plan 9's network filesystem, studies suggest using synthetic filesystems as universal access scheme to that information. The major benefit is that 9P is very simple and so quite easy to implement in hardware and can be easily used and over virtually any kind of network (from a serial link up to the internet).
Pros and cons
The major argument for using synthetic filesystems might be the flexibility and easy access to
service-oriented architectures. Once a noticeable number of applications use this scheme, the overall overhead (code, resource consumption, maintenance work) can be reduced significantly. Many general arguments for SOAs also apply here.
Arguments against synthetic filesystems include the fact that filesystem semantics may not fit all application scenarios. For example, complex
remote procedure calls with many parameters tend to be hard to map to filesystem schemes, and may require application redesign.
References
External links
The 9P synthetic-file-system protocol
* BROWN, Geoffrey
On-Chip Filesystems to support Complex Embedded Systems* PISUPATI, Bhani N.
A virtual filesystem framework to support embedded software development* Minnich, Ron
Why Plan9 is not dead And What we can learn from it
{{Operating system
Special-purpose file systems