In computing, a device driver is a computer program that operates or controls a particular type of device that is attached to a computer or automaton.[1] 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 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.
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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.[1] Programmers can write higher-level application code independently of whatever specific hardware the end-user is using.For example, 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 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 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.[3]
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 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 optimum 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 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.
In Linux environments, programmers can build device drivers as parts of 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).[4]
Microsoft Windows .sys files and Linux .ko files can contain loadable device drivers. The advantage of loadable device drivers is that they can be loaded only when necessary and then unloaded, thus saving kernel memory.
Device drivers, particularly on modern[update] Microsoft Windows platforms, can run in kernel-mode (Ring 0 on x86 CPUs) or in user-mode (Ring 3 on x86 CPUs).[5] The primary benefit of running a driver in user mode is improved stability, since a poorly written user-mode device driver cannot crash the system by overwriting kernel memory.[6] On the other hand, user/kernel-mode transitions usually impose a considerable performance overhead, thus making kernel-mode drivers preferred for low-latency networking.
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 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 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.
Devices often have a large number of diverse and customized device drivers running in their operating system (OS) kernel and often contain various bugs and vulnerabilities, making them a target for exploits.[16] Bring Your Own Vulnerable Driver (BYOVD) uses signed, old drivers that contain flaws that allow hackers to insert malicious code into the kernel.[17]
There is a lack of effective kernel vulnerability detection tools, especially for closed-source OSes such as Microsoft Windows[18] where the source code of the device drivers is mostly not public (open source)[19] and the drivers often also have many privileges.[20][21][22][23]
A group of security researchers considers the lack of isolation as one of the main factors undermining kernel security,[29] and published a isolation framework to protect operating system kernels, primarily the monolithic Linux kernel which, according to them, gets ~80,000 commits/year to its drivers.[30][31]
It's challenging to give a single precise definition for the term driver. In the most fundamental sense, a driver is a software component that lets the operating system and a device communicate with each other.
For example, suppose an application needs to read some data from a device. The application calls a function implemented by the operating system, and the operating system calls a function implemented by the driver. The driver, which was written by the same company that designed and manufactured the device, knows how to communicate with the device hardware to get the data. After the driver gets the data from the device, it returns the data to the operating system, which returns it to the application.
For a given I/O request (like reading data from a device), there are often several drivers layered in a driver stack that participate in the request. The conventional way to visualize the stack is with the first participant at the top and the last participant at the bottom, as shown in this diagram. Some of the drivers in the stack might participate by transforming the request from one format to another. These drivers don't communicate directly with the device; they just manipulate the request and pass the request along to drivers that are lower in the stack.
Some filter drivers observe and record information about I/O requests but don't actively participate in them. For example, certain filter drivers act as verifiers to make sure the other drivers in the stack are handling the I/O request correctly.
For example, suppose you need to write a tool that has access to core operating system data structures. These structures can only be accessed by code running in kernel mode. You can do that by splitting the tool into two components. The first component runs in user mode and presents the user interface. The second component runs in kernel mode and has access to the core operating system data. The component that runs in user mode is called an application, and the component that runs in kernel mode is called a software driver. A software driver isn't associated with a hardware device.
Software drivers always run in kernel mode. The main reason for writing a software driver is to gain access to protected data that is available only in kernel mode. However device drivers don't always need access to kernel-mode data and resources. So some device drivers run in user mode.
Our explanation so far oversimplifies the definition of function driver. We said that the function driver for a device is the one driver in the stack that communicates directly with the device. This is true for a device that connects directly to the Peripheral Component Interconnect (PCI) bus. The function driver for a PCI device obtains addresses that are mapped to port and memory resources on the device. The function driver communicates directly with the device by writing to those addresses.
However in many cases, a device doesn't connect directly to the PCI bus. Instead the device connects to a host bus adapter that is connected to the PCI bus. For example, a USB toaster connects to a host bus adapter (called a USB host controller), which is connected to the PCI bus. The USB toaster has a function driver, and the USB host controller also has a function driver. The function driver for the toaster communicates indirectly with the toaster by sending a request to the function driver for the USB host controller. The function driver for the USB host controller then communicates directly with the USB host controller hardware, which communicates with the toaster.
Computers crash for many reasons. Your machine may suffer performance issues due to a faulty component, an inadequate power supply, or defective hardware, or it may crash because of a malware infection (you can check by using a free antivirus scan). But you may also see the Blue Screen of Death (BSoD) due to malfunctioning computer drivers. In fact, most crashes occur because of bad drivers (double entendre not intended). be457b7860
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