Extensibility is a software engineering and systems design principle that provides for future growth. Extensibility is a measure of the ability to extend a system and the level of effort required to implement the extension. Extensions can be through the addition of new functionality or through modification of existing functionality. The principle provides for enhancements without impairing existing system functions.
39-470: An extensible system is one whose internal structure and dataflow are minimally or not affected by new or modified functionality, for example recompiling or changing the original source code might be unnecessary when changing a system’s behavior, either by the creator or other programmers. Because software systems are long lived and will be modified for new features and added functionalities demanded by users, extensibility enables developers to expand or add to
78-618: A message-based protocol for communicating with their devices—as user-mode drivers. If such drivers malfunction, they do not cause system instability. The Kernel-Mode Driver Framework (KMDF) model continues to allow development of kernel-mode device drivers, but attempts to provide standard implementations of functions that are known to cause problems, including cancellation of I/O operations, power management, and plug and play device support. Apple has an open-source framework for developing drivers on macOS , called I/O Kit. In Linux environments, programmers can build device drivers as parts of
117-487: A high-level application for interacting with a serial port may simply have two functions for "send data" and "receive data". At a lower level, a device driver implementing these functions would communicate to the particular serial port controller installed on a user's computer. The commands needed to control a 16550 UART are much different from the commands needed to control an FTDI serial port converter, but each hardware-specific device driver abstracts these details into
156-463: A specific deployment scenario off-the-rack, taking third party users other than the manufacturer into consideration. Many software systems and software product-lines are derived from a base system, which share a common software architecture or sometimes large parts of the functionality and implementation but are possibly equipped with different components that require an extensible base system. Building software systems that are independently extensible
195-437: A target for exploits . Bring Your Own Vulnerable Driver (BYOVD) uses signed, old drivers that contain flaws that allow hackers to insert malicious code into the kernel. Drivers that may be vulnerable include those for WiFi and Bluetooth, gaming/graphics drivers, and drivers for printers. There is a lack of effective kernel vulnerability detection tools, especially for closed-source OSes such as Microsoft Windows where
234-437: A technology to be transferred to another project with less development and maintenance time, as well as enhanced reliability and consistency. Modern operating systems support extensibility through device drivers and loadable kernel modules . Many modern applications support extensibility through plug-ins , extension languages , applets , etc. The trend of increasing extensibility negatively affects software security. CGI
273-408: Is a software paradigm based on the idea of representing computations as a directed graph , where nodes are computations and data flow along the edges. Dataflow can also be called stream processing or reactive programming . There have been multiple data-flow/stream processing languages of various forms (see Stream processing ). Data-flow hardware (see Dataflow architecture ) is an alternative to
312-402: Is an important challenge. An independently extensible system not only allows two people to independently develop extensions to the system, but also allows the two extensions to be combined without a global integrity check. There are three different forms of software extensibility: white-box extensibility, gray-box extensibility, and black-box extensibility, which are based on what artifacts and
351-408: Is directly being hacked into. It requires available source code and the modification permitted source code license. Open-box extensibility is most relevant to bug fixing, internal code refactoring, or production of next version of a software product. Glass-box extensibility (also called architecture driven frameworks) allows a software system to be extended with available source code, but may not allow
390-563: Is important that the hardware manufacturer provide information on how the device communicates. Although this information can instead be learned by reverse engineering , this is much more difficult with hardware than it is with software. Microsoft has attempted to reduce system instability due to poorly written device drivers by creating a new framework for driver development, called Windows Driver Frameworks (WDF). This includes User-Mode Driver Framework (UMDF) that encourages development of certain types of drivers—primarily those that implement
429-407: Is improved stability, since a poorly written user-mode device driver cannot crash the system by overwriting kernel memory. Because of the diversity of modern hardware and operating systems, drivers operate in many different environments. Drivers may interface with: Common levels of abstraction for device drivers include: So choosing and installing the correct device drivers for given hardware
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#1733085511569468-412: Is more limited than the various white-box approaches. Black-box extensions are typically achieved through system configuration applications or the use of application-specific scripting languages by defining components interfaces. Gray-box extensibility is a compromise between a pure white-box and a pure black-box approach, which does not rely fully on the exposure of source code. Programmers could be given
507-472: Is often a key component of computer system configuration. Virtual device drivers represent a particular variant of device drivers. They are used to emulate a hardware device, particularly in virtualization environments, for example when a DOS program is run on a Microsoft Windows computer or when a guest operating system is run on, for example, a Xen host. Instead of enabling the guest operating system to dialog with hardware, virtual device drivers take
546-482: Is one of the primary means by which web servers provide extensibility. Some people see CGI scripts as "an enormous security hole". [REDACTED] The dictionary definition of extensibility at Wiktionary Dataflow In computing , dataflow is a broad concept, which has various meanings depending on the application and context. In the context of software architecture , data flow relates to stream processing or reactive programming . Dataflow computing
585-421: Is provided instead. Small commands are made to prevent losing the element of extensibility, following the principle of separating work elements into comprehensible units, in order to avoid traditional software development issues including low cohesion and high coupling and allow for continued development. Embracing change is essential to the extensible design, in which additions will be continual. Each chunk of
624-504: Is that they can be loaded only when necessary and then unloaded, thus saving kernel memory. Depending on the operating system, device drivers may be permitted to run at various different privilege levels . The choice of which level of privilege the drivers are in is largely decided by the type of kernel an operating system uses. An operating system which uses a monolithic kernel , such as the Linux kernel , will typically run device drivers with
663-400: Is via protection rings . On many systems, such as those with x86 and ARM processors, switching between rings imposes a performance penalty, a factor that operating system developers and embedded software engineers consider when creating drivers for devices which are preferred to be run with low latency, such as network interface cards . The primary benefit of running a driver in user mode
702-609: The PCI bus or USB is identified by two IDs which consist of two bytes each. The vendor ID identifies the vendor of the device. The device ID identifies a specific device from that manufacturer/vendor. A PCI device has often an ID pair for the main chip of the device, and also a subsystem ID pair that identifies the vendor, which may be different from the chip manufacturer. Computers often have many diverse and customized device drivers running in their operating system (OS) kernel which often contain various bugs and vulnerabilities , making them
741-405: The interrupt handling required for any necessary asynchronous time-dependent hardware interface. The main purpose of device drivers is to provide abstraction by acting as a translator between a hardware device and the applications or operating systems that use it. Programmers can write higher-level application code independently of whatever specific hardware the end-user is using. For example,
780-525: The kernel , separately as loadable modules , or as user-mode drivers (for certain types of devices where kernel interfaces exist, such as for USB devices). Makedev includes a list of the devices in Linux, including ttyS (terminal), lp ( parallel port ), hd (disk), loop, and sound (these include mixer , sequencer , dsp , and audio). Microsoft Windows .sys files and Linux .ko files can contain loadable device drivers. The advantage of loadable device drivers
819-422: The basis of all software because of human phenomena since software is an "evolving entity" which is developed and maintained by human beings, yielding ongoing system changes in software specification and implementation. Components of a software are often developed and deployed by unrelated parties independently. Adaptable software components are necessary since components from external vendors are unlikely to fit into
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#1733085511569858-619: The classic von Neumann architecture . The most obvious example of data-flow programming is the subset known as reactive programming with spreadsheets. As a user enters new values, they are instantly transmitted to the next logical "actor" or formula for calculation. Distributed data flows have also been proposed as a programming abstraction that captures the dynamics of distributed multi-protocols. The data-centric perspective characteristic of data flow programming promotes high-level functional specifications and simplifies formal reasoning about system components. Hardware architectures for dataflow
897-528: The code to be modified. Extensions have to be separated from the original system in a way that the original system is not affected. One example of this form of extensibility is object-oriented application frameworks which achieve extensibility typically by using inheritance and dynamic binding. In black-box extensibility (also called data-driven frameworks) no details about a system’s implementation are used for implementing deployments or extensions; only interface specifications are provided. This type of approach
936-571: The data is represented by a series of shapes and lines. Dataflow can also refer to: [REDACTED] The dictionary definition of dataflow at Wiktionary Device driver In the context of an operating system , a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton . A driver provides a software interface to hardware devices, enabling operating systems and other computer programs to access hardware functions without needing to know precise details about
975-662: The design of their hardware. Moreover, it was traditionally considered in the hardware manufacturer 's interest to guarantee that their clients can use their hardware in an optimal way. Typically, the Logical Device Driver (LDD) is written by the operating system vendor, while the Physical Device Driver (PDD) is implemented by the device vendor. However, in recent years, non-vendors have written numerous device drivers for proprietary devices, mainly for use with free and open source operating systems . In such cases, it
1014-461: The hardware being used. A driver communicates with the device through the computer bus or communications subsystem to which the hardware connects. When a calling program invokes a routine in the driver, the driver issues commands to the device (drives it). Once the device sends data back to the driver, the driver may invoke routines in the original calling program. Drivers are hardware dependent and operating-system-specific. They usually provide
1053-446: The opposite role and emulates a piece of hardware, so that the guest operating system and its drivers running inside a virtual machine can have the illusion of accessing real hardware. Attempts by the guest operating system to access the hardware are routed to the virtual device driver in the host operating system as e.g., function calls . The virtual device driver can also send simulated processor-level events like interrupts into
1092-432: The processes are determinate . This implies that each determinate process computes a continuous function from input streams to output streams, and that a network of determinate processes is itself determinate, thus computing a continuous function. This implies that the behavior of such networks can be described by a set of recursive equations, which can be solved using fixed point theory . The movement and transformation of
1131-410: The rest of the system. Even drivers executing in user mode can crash a system if the device is erroneously programmed . These factors make it more difficult and dangerous to diagnose problems. The task of writing drivers thus usually falls to software engineers or computer engineers who work for hardware-development companies. This is because they have better information than most outsiders about
1170-499: The same (or similar) software interface. Writing a device driver requires an in-depth understanding of how the hardware and the software works for a given platform function. Because drivers require low-level access to hardware functions in order to operate, drivers typically operate in a highly privileged environment and can cause system operational issues if something goes wrong. In contrast, most user-level software on modern operating systems can be stopped without greatly affecting
1209-509: The same privilege as all other kernel objects. By contrast, a system designed around microkernel , such as Minix , will place drivers as processes independent from the kernel but that use it for essential input-output functionalities and to pass messages between user programs and each other. On Windows NT , a system with a hybrid kernel , it is common for device drivers to run in either kernel-mode or user-mode . The most common mechanism for segregating memory into various privilege levels
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1248-580: The simple tags could not differentiate between them. Designs that use content-addressable memory are called dynamic dataflow machines by Arvind . They use tags in memory to facilitate parallelism. Data flows around the computer through the components of the computer. It gets entered from the input devices and can leave through output devices (printer etc.). A dataflow network is a network of concurrently executing processes or automata that can communicate by sending data over channels (see message passing .) In Kahn process networks , named after Gilles Kahn ,
1287-410: The software’s capabilities and facilitates systematic reuse. Some of its approaches include facilities for allowing users’ own program routines to be inserted and the abilities to define new data types as well as to define new formatting markup tags. Extensible design in software engineering is to accept that not everything can be designed in advance. A light software framework which allows for changes
1326-452: The source code of the device drivers is mostly not public (open source) and drivers often have many privileges. A group of security researchers considers the lack of isolation as one of the main factors undermining kernel security , and published an isolation framework to protect operating system kernels, primarily the monolithic Linux kernel whose drivers they say get ~80,000 commits per year. An important consideration in
1365-574: The system will be workable with any changes, and the idea of change through addition is the center of the whole system design. Extensible design supports frequent re-prioritization and allows functionality to be implemented in small steps upon request, which are the principles advocated by the Agile methodologies and iterative development. Extensibility imposes fewer and cleaner dependencies during development, as well as reduced coupling and more cohesive abstractions, plus well defined interfaces. Fickleness lies at
1404-477: The system’s specialization interface which lists all available abstractions for refinement and specifications on how extensions should be developed. Extensibility and reusability have many emphasized properties in common, including low coupling, modularity and high risk elements’ ability to construct for many different software systems, which is motivated by the observation of software systems often sharing common elements. Reusability together with extensibility allows
1443-451: The virtual machine. Virtual devices may also operate in a non-virtualized environment. For example, a virtual network adapter is used with a virtual private network , while a virtual disk device is used with iSCSI . A good example for virtual device drivers can be Daemon Tools . There are several variants of virtual device drivers, such as VxDs , VLMs , and VDDs. Solaris descriptions of commonly used device drivers: A device on
1482-412: The way they are changed. Under this form of extensibility, a software system can be extended by modifying the source code , and it is the most flexible and the least restrictive form. There are two sub-forms of extensibility, open-box extensibility and glass-box extensibility, depending on how changes are applied. Changes are performed invasively in open-box extensible systems; i.e. original source code
1521-484: Was a major topic in computer architecture research in the 1970s and early 1980s. Jack Dennis of the Massachusetts Institute of Technology (MIT) pioneered the field of static dataflow architectures. Designs that use conventional memory addresses as data dependency tags are called static dataflow machines. These machines did not allow multiple instances of the same routines to be executed simultaneously because
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