Method and system for configuring and executing device drivers based on configuration requirements

Claims

We claim:

1. A method in a computer system for configuring a device driver from a plurality of component drivers by determining whether each of the plurality of component drivers should be included in the device driver, the method comprising the computer-implemented steps of:

for each selected one of the plurality of component drivers,

determining configuration requirements imposed by each of the component drivers that is already included in the device driver;

determining whether the selected component driver satisfies at least one of the determined configuration requirements imposed by the component drivers that are already included in the device driver; and

when the selected component driver satisfies at least one of the determined configuration requirements, including the selected component driver in the device driver.

2. The method of claim 1, wherein the step of determining whether the selected component driver satisfies at least one of the determined configuration requirements includes the step of invoking the selected component driver and having the invoked selected component driver determine whether the invoked selected component driver satisfies one of the determined configuration requirements.

3. The method of claim 2 wherein the step of including the selected component driver in the device driver includes the step of, when the invoked selected component driver satisfies at least one of the determined configuration requirements, the invoked selected component driver include the invoked selected component driver in the device driver.

4. The method of claim 1,

wherein the step of including the selected component driver in the device driver includes the step of including the selected component driver as a layer in the device driver;

wherein a first of the component drivers that is included in the device driver comprises a bottom layer of the device driver;

wherein each additional one of the component drivers that is included in the device driver comprises a higher layer of the device driver; and

wherein a last of the component drivers that is included in the device driver comprises a top layer of the device driver.

5. A method in a computer system for configuring and executing a device driver, the device driver being configured from a plurality of component drivers by determining whether each of the plurality of component drivers should be included in the device driver, each of the plurality of component drivers performing a function, the method comprising the computer-implemented steps of:

for each selected one of the plurality of component drivers,

determining configuration requirements imposed by each of the component drivers that is already included in the device driver;

determining whether the selected component driver satisfies at least one of the determined configuration requirements imposed by the component drivers that are already included in the device driver; and

when the selected component driver satisfies at least one of the determined configuration requirements, including the selected component driver in the device driver; and

invoking and performing the function of each component driver that is part of the device driver.

6. The method of claim 5,

wherein the step of determining whether the selected component driver satisfies at least one of the determined configuration requirements includes the step of invoking the selected component driver and having the invoked selected component driver determine whether the invoked selected component driver satisfies at least one of the determined configuration requirements; and

wherein the step of including the selected component driver in the device driver includes the step of, when the invoked selected component driver satisfies at least one of the determined configuration requirements, having the invoked selected component driver include the invoked selected component driver in the device driver.

7. The method of claim 5,

wherein the step of including the selected component driver in the device driver includes the step of including the selected component driver as a layer in the device driver;

wherein a first one of the component drivers that is included in the device driver comprises a bottom layer of the device driver;

wherein each additional one of the component drivers that is included in the device driver comprises a higher layer of the device driver; and

wherein a last of the component drivers that is included in the device driver comprises a top layer of the device driver.

8. The method of claim 7, wherein each component driver included in the device driver invokes the next lower layer component driver until the bottom layer component driver has been invoked.

9. A computer system for configuring a device driver from a plurality of component drivers by determining whether each selected one of the plurality of component drivers should be included in the device driver, the computer system comprising:

a plurality of component drivers;

a component driver selection routine for performing the following steps for each selected component driver:

determining configuration requirements imposed by each of the component drivers that is already included in the device driver;

determining whether the selected component driver satisfies one of the determined configuration requirements; and

when the selected component driver satisfies at least one of the determined configuration requirements, including the component driver in the device driver.

10. The method of claim 1, further including the step of, for each given component driver included in the device driver, indicating the configuration requirements of any component driver that is already included in the device driver that the given component driver satisfies.

11. The method of claim 1, further including the step of, for each component driver included in the device driver, indicating any configuration requirements that the component driver must have satisfied by another component driver included in the device driver.

12. The method of claim 5, further including the step of, for each component driver included in the device driver, indicating the configuration requirements imposed by any component driver that is already included in the device driver that the component driver satisfies.

13. The method of claim 5, further including the step of, for each component driver included in the device driver, indicating any configuration requirements that the component driver must have satisfied by another component driver included in the device driver.

14. A method in a computer system for configuring a device driver from a plurality of component drivers by determining whether each of the plurality of component drivers should be included in the device driver, the device driver corresponding to a device, the method comprising the computer-implemented steps of:

determining a type of the device; and

for each selected one of the plurality of component drivers,

determining configuration requirements imposed by each of the component drivers that is already included in the device driver and not satisfied by any other of the component drivers that are already included in the device driver;

determining whether the selected component driver should be included in the device driver based on the determined type of the device and the determined configuration requirements; and

including the selected component driver in the device driver when the selected component driver relates to the determined type of the device or when the selected component driver satisfies any of the determined configuration requirements.

15. The method of claim 14,

further including the step of invoking each of the plurality of component drivers;

wherein the step of determining configuration requirements includes the step of having the invoked selected component driver determine configuration requirements imposed by each of the component drivers that is already included in the device driver and not satisfied by any other of the component drivers that are already included in the device driver;

wherein the step of determining whether the selected component driver should be included in the device driver includes the step of having the invoked selected component driver determine whether the invoked selected component driver should be included in the device driver based on the determined type of the device and the determined configuration requirements; and

wherein the step of including the selected component driver in the device driver includes the step of having the invoked selected component driver include the invoked component driver in the device driver when the invoked selected component driver relates to the determined type of the device or when the invoked selected component driver satisfies any of the determined configuration requirements.

16. The method of claim 14, further including the step of, for each given one of the component drivers that is included in the device driver, indicating the configuration requirements of any of the component drivers that are already included in the device driver that the given component driver satisfies.

17. The method of claim 14, further including the step of, for each given one of the component drivers that is included in the device driver, indicating any configuration requirements that the given component driver must have satisfied by another one of the component drivers that is included in the device driver.

18. The method of claim 14,

wherein the step of including the component driver in the device driver includes the step of including the component driver as a layer in the device driver;

wherein a first of the component drivers that is included in the device driver comprises a bottom layer of the device driver;

wherein each additional of the component drivers that is included in the device driver comprises a higher layer of the device driver; and

wherein a last of the component drivers that is included in the device driver comprises a top layer of the device driver.

19. The method of claim 18, further including the steps of, for each given one of the component drivers that is included in the device driver,

indicating the configuration requirements of ones of the component drivers, that are at lower layers of the device driver than the given component driver, that the given component driver satisfies; and

indicating any configuration requirements that the given component driver must have satisfied by ones of the component drivers that are at higher layers of the device driver than the given component driver.

20. A method in a computer system for executing a device driver, the device driver being configured from a plurality of component drivers, the component drivers imposing configuration requirements, each of the plurality of component drivers performing a function, at least one component driver being included in the device driver, the method comprising the computer-implemented steps of:

determining whether the configuration requirements imposed by each component driver included in the device driver have been satisfied; and

when the configuration requirements have been satisfied, invoking and performing the function of each of the component drivers that is included in the device driver.

21. A method in a computer system for executing a device driver, the device driver being configured from a plurality of component drivers, the component drivers imposing configuration requirements, each of the plurality of component drivers performing a function, at least two component drivers being part of the device driver, the component drivers comprising layers in the device driver, a first of the component drivers that is included in the device driver comprising a bottom layer, each additional one of the component drivers that is included in the device driver comprising a higher layer, and a last of the component drivers that is included in the device driver comprising a top layer, the method comprising the computer-implemented steps of:

determining whether the configuration requirements imposed by each of the component drivers that is included in the device driver have been satisfied; and

when the configuration requirements have been satisfied, for each given one of component drivers that is included in the device driver starting with the component driver at the top layer of the device driver,

invoking the given component driver; and

performing the function of the given component driver.

22. The method of claim 21 wherein each of the component drivers that is included in the device driver invokes one of the component drivers at a next lower layer in the device driver until the component driver at the bottom layer of the device driver has been invoked.

23. A method in a computer system for configuring and executing a device driver, the device driver being configured from a plurality of component drivers by determining whether each of the plurality of component drivers should be included in the device driver, each of the plurality of component drivers performing a function, the device driver corresponding to a device, the method comprising the computer-implemented steps of:

determining a type of the device;

for each selected one of the plurality of component drivers,

determining configuration requirements imposed by each of the component drivers that is already included in the device driver and not satisfied by any other of the component drivers that are already included in the device driver;

determining whether the selected component driver should be included in the device driver based on the determined type of the device and the determined configuration requirements; and

including the selected component driver in the device driver when the selected component driver relates to the determined type of the device or when the selected component driver satisfies any of the determined configuration requirements;

determining whether the configuration requirements imposed by each of the component drivers that is included in the device driver have been satisfied; and

when the configuration requirements have been satisfied, invoking and performing the function of each of the component drivers that is included in the device driver.

24. The method of claim 23,

further including the step of invoking each selected one of the plurality of component drivers to determine whether the selected component driver should be included in the device driver;

wherein the step of determining configuration requirements includes the step of having the invoked selected component driver determine configuration requirements imposed by each of the component drivers that is already included in the device driver and not satisfied by any other ones of the component drivers that are already included in the device driver;

wherein the step of determining whether the selected component driver should be included in the device driver includes the step of having the invoked selected component driver determine whether the invoked component selected driver should be included in the device driver based on the determined type of the device and the determined configuration requirements; and

wherein the step of including the selected component driver part of the device driver includes the step of having the invoked selected component driver include the invoked selected component driver in the device driver when the invoked selected component driver relates to the determined type of the device or when the invoked selected component driver satisfies any of the determined configuration requirements.

25. The method of claim 23, further including the step of, for each given one of the component drivers that is included in the device driver, indicating the configuration requirements imposed by any of the component drivers that are already included in the device driver that the given component driver satisfies.

26. The method of claim 23, further including the step of, for each given one of the component drivers that is included in the device driver, indicating any configuration requirements that the given component driver must have satisfied by another of the component drivers that is included in the device driver.

27. The method of claim 23,

wherein the step of making the selected component driver part of the device driver includes the step of including the selected component driver as a layer in the device driver;

wherein a first of the component drivers that is included in the device driver comprises a bottom layer of the device driver;

wherein each additional one of the component drivers that is included in the device driver comprises a higher layer of the device driver; and

wherein a last of the component drivers that is included in the device driver comprises a top layer of the device driver.

28. The method of claim 27, further including the steps of, for each given one of the component drivers that is included in the device driver,

indicating the configuration requirements of ones of the component drivers, at layers of the device driver that are lower than the layer of the given component driver, that the component driver satisfies; and

indicating any configuration requirements that the given component driver must have satisfied by component drivers at layers in the device driver that are higher than the layer of the given component driver.

29. The method of claim 27 wherein the step of, for each given one of the component drivers that are included in the device driver, invoking the component driver includes the step of, for each given one of the component drivers that is included in the device drivers, starting with the component driver at the top layer of the device driver, invoking the given component driver.

30. The method of claim 29 wherein each component driver included in the device driver invokes the component driver at the next lower layer of the device driver until the component driver at the bottom layer has been invoked.

31. A computer system comprising:

a device;

a device driver for the device;

a plurality of component drivers tier possible incorporation into the device driver; and

a component driver selection routine for determining whether each selected one of the component drivers should be made part of the device driver, said routine performing the steps of:

determining the type of the device;

determining configuration requirements imposed by each of the component drivers that is already included in the device driver and not satisfied by any other of the component drivers that are already included in the device driver;

determining whether the selected component driver should be included in the device driver based on the determined type of the device and the determined configuration requirements; and

including the selected component driver in the device driver when the selected component driver relates to the determined type of the device or when the selected component driver satisfies any of the determined configuration requirements.

32. The computer system of claim 31, further comprising a device driver configuration routine for invoking each of the plurality of component drivers so that each invoked component driver can execute the component driver selection routine.

33. A computer system for executing a device driver, the device driver being configured from a plurality of component drivers, the component drivers imposing configuration requirements, each of the plurality of component drivers performing a function, the system comprising:

at least one of the component drivers being included in the device driver for performing the component driver function; and

an input-output system for:

determining whether the configuration requirements imposed by each of the component drivers that is included in the device driver have been satisfied; and

when the configuration requirements have been satisfied, for each given one of the component drivers that is included in the device driver, invoking the given component driver.

34. A method in a computer system for configuring a computer module from a plurality of component routines by determining whether each of the plurality of component routines should be included in the computer module, the method comprising the computer-implemented steps of:

for each selected one of the plurality of component routines,

determining configuration requirements imposed by each of the component routines that is already included in the computer module;

determining whether the selected component routine satisfies a determined configuration requirement; and

when the selected component routine satisfies one of the determined configuration requirements, including the component routine in the computer module.

35. The method of claim 34 wherein the step of determining whether the selected component routine satisfies one of the determined configuration requirements includes the step of invoking the selected component routine and having the invoked selected component routine determine whether the invoked selected component routine satisfies one of the determined configuration requirements.

36. The method of claim 35 wherein the step of including the component routine in the computer module includes the step of, when the invoked selected component routine satisfies one of the determined configuration requirements, having the invoked selected component routine include the invoked selected component routine in the computer module.

37. The method of claim 34,

wherein the step of including the selected component routine in the computer module includes the step of including the selected component routine as a layer in the computer module;

wherein a first of the component routines that is included in the computer module comprises a bottom layer of the computer module;

wherein each additional one of the component routines that is included in the computer module comprises a higher layer of the computer module; and

wherein a last of the component routines that is included in the computer module comprises a top layer of the computer module.

38. A method in a computer system for configuring and executing a computer program, the computer program being configured from a plurality of component programs by determining whether each of the plurality of component programs should be included in the computer program, each of the plurality of component programs performing a function, the method comprising the computer-implemented steps of:

for each selected one of the plurality of component programs,

determining configuration requirements imposed by each of the component programs that is already included in the computer program;

determining whether the selected component program satisfies any of the determined configuration requirements; and

when the selected component program satisfies at least one of the determined configuration requirements, including the selected component program in the computer program; and

invoking and performing the function of each selected component program that are included in the computer program.

39. The method of claim 38,

wherein the step of determining whether the selected component program satisfies one of the determined configuration requirements includes the step of invoking the selected component program and having the invoked selected component program determine whether the invoked selected component program satisfies at least one of the determined configuration requirements; and

wherein the step of including the selected component program in the computer program includes the step of, when the invoked selected component program satisfies one of the determined configuration requirements, having the invoked selected component program include the invoked selected component program in the computer program.

40. The method of claim 38,

wherein the step of including the selected component program in the computer program includes the step of including the selected component program as a layer in the computer program;

wherein a first of the component programs that is included in the computer program comprises a bottom layer of the computer program;

wherein each additional one of the component programs that is included in the computer program comprises a higher layer of the computer program; and

wherein a last of the component programs that is included in the computer program comprises a top layer of the computer program.

41. A computer system for configuring a computer module from a plurality of component routines by determining whether each of the plurality of component routines should be included in the computer module, the computer system comprising:

a plurality of component routines;

a component routine selector for performing the following steps for each of selected one of the component routines:

determining configuration requirements imposed by each of the component routines that is already included in the computer module;

determining whether the selected component routine satisfies at least one of the determined configuration requirements; and

when the selected component routine satisfies one of the determined configuration requirements, including the selected component routine in the computer module.

TECHNICAL FIELD

The present invention relates generally to the field of device drivers and, more particularly, to a method and system for configuring and executing device drivers.

BACKGROUND OF THE INVENTION

A computer system typically is connected to various peripheral devices, which may include disk drives, tape drives, printers, and modems. The computer system has an operating system that provides an interface between an application program and these devices. The operating system receives from the application program a request to access one of the devices and translates this request into a request that will be understandable by that device. The operating system sends the translated request to the device and typically informs the application program when the requested access is complete.

The portion of the operating system that translates a request to access a device and controls communications with that device is typically referred to as a device driver. For example, an application program may request the operating system to read a file stored on a disk drive. The operating system would invoke a device driver provided for the disk drive and send the device driver this read request. The disk device driver would translate the read request by determining the actual disk location at which the file is stored, and would send the read request to the disk drive. The disk drive would then service the read request by reading the disk at the determined actual disk location, and then inform the device driver upon completion. The device driver would then inform the application program that the request has been serviced.

FIG. 1 is a block diagram illustrating the prior art use of a device driver in a computer system. The computer system comprises a computer 100 and a plurality of devices 113, 114, 115. The computer 100 includes a memory loaded with various application programs 101 and an operating system 102. The application programs 101 request services of the devices through the operating system 102. The operating system 102 receives such a request and invokes an appropriate device driver 103, 104, 105 to service the request. The device driver 103, 104, 105 then translates the request and sends it to the device 113, 114, 115, respectively. It should be noted that, although a device driver can correspond to any number of devices, only one device for each device driver is shown for simplicity of explanation.

Prior device drivers typically have been developed by the manufacturer of each corresponding device. The developer of the operating system typically publishes a specification of the interface between the operating system and a device driver. The manufacturer of the device then develops the device driver necessary to communicate with its corresponding device using this specification. The manufacturer then distributes the device driver to its customers.

After developing the device driver, the manufacturer of the device will often add various features to the device driver to enhance the marketability of the device. For example, a manufacturer of a disk drive may provide a device driver with data compression, data encryption, or disk caching options. Unfortunately, as more options are added to the device driver, the device driver becomes more complex. As the complexity of a device driver increases, the more difficult it becomes for a manufacturer to modify and test the device driver. For example, the addition of data compression, data encryption or disk caching typically requires changes to be made throughout the device driver code in order to accommodate these options.

An additional problem is that the complexity of distributing device drivers increases when the device manufacturer integrates third party software into its device driver. For example, if a third party develops a particularly efficient data compression program, the third party developer may sell the program to various device manufacturers. Each manufacturer would then integrate the data compression program into its own device driver. Once the integration is complete, each manufacturer would then distribute its new device driver directly to its customers or indirectly through the operating system developer when a new version of the operating system is released.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and system in which a device driver is dynamically configured.

It is another object of the present invention to provide a method and system for organizing a device driver into layers of component drivers, each of which imposes configuration requirements during configuration of the device driver.

It is another object of the present invention to provide a method and system for configuring a device driver based on configuration requirements of component drivers which compose the device driver.

It is another object of the present invention to provide a method and system in which a device driver can be configured to include new features without the need for the device manufacturer to integrate the new features.

It is another object of the present invention to provide a method and system in which new features developed by third parties can be dynamically configured into a device driver.

It is another object of the present invention to provide a method and system for configuring a device driver based on configuration requirements of new features provided.

It is another object of the present invention to provide a method and system wherein access to a device is allowed only when all configuration requirements of the device driver have been satisfied.

These and other objects, which will become apparent as the invention is more fully described below, are obtained by a method and system for configuring a device driver described as follows. In a preferred embodiment, the device driver is organized in layers of component drivers that each perform a function (e.g., disk caching) used in accessing a device. When accessing a device, a top layer component driver of the device driver is first invoked. Each component driver performs its function and potentially invokes a next lower layer component driver down to a bottom layer component driver.

A device driver is configured by first selecting a component driver to be included as the bottom layer and continuing to select higher level component drivers until the top layer component driver is included. In a preferred embodiment, at computer startup or restart, the operating system invokes each component driver to determine whether to select the component driver to be included as a layer in the device driver. Each component driver is or is not selected according to existing device-specific information based on characteristics of the device and, in some cases, based on configuration requirements of component drivers previously included as lower layers. Each selected component driver indicates those configuration requirements that it satisfies, and indicates any configuration requirements to be imposed on component drivers yet to be included as higher layers.

When a component driver is selected, it stores a reference to itself in a call-down table for the device driver. The call-down table stores the order in which the selected component drivers are invoked. When accessing a device, the operating system first invokes the component driver identified by the top reference in the call-down table for that device. Each component driver in turn potentially invokes the component driver identified by the next lower reference in the call-down table. The component drivers identified in the call-down table are typically only invoked to perform the device access if all configuration requirements have been met in configuring the device driver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the prior art use of a device driver in a computer system.

FIG. 2 is a block diagram illustrating components of the present invention.

FIG. 3 is a block diagram showing a sample disk drive device driver.

FIG. 4 is a block diagram illustrating the data structures that support the selection and configuring of component drivers.

FIG. 5 is a flow diagram of the request routine performed by the Input/Output System in the present invention.

FIG. 6 is a flow diagram of the execution of a sample component driver.

FIG. 7 is a block diagram illustrating how the driver configuration routine is performed by the Input/Output System in the present invention.

FIG. 8 is a block diagram showing a call-down table entry in the call-down table and a device-type entry in the device control block.

FIG. 9 is a flow diagram of a device driver configuration routine.

FIG. 10 is a flow diagram of a component driver selection routine.

FIGS. 11A and 11B are block diagrams illustrating sample configurations of various device drivers.

FIGS. 12A and 12B are block diagrams showing the contents of the call-down table corresponding to different configurations of a device driver.

DETAILED DESCRIPTION OF THE INVENTION

The present invention configures a device driver by selecting appropriate component drivers to be included as layers in the device driver. During configuration, starting with a bottom layer and continuing to a top layer, each component driver is selected or not selected based on device-specific information and potentially based on configuration requirements of previously included lower layer component drivers.

Each selected component driver indicates configuration requirements that must be satisfied by higher layers. Each component driver also indicates lower layers' configuration requirements that it satisfies. When an application program requests access to a device, the selected component drivers are invoked to perform the device access only if all of these configuration requirements have been satisfied.

As an example, a component driver that requires physical disk addressing (e.g. sector number) would indicate a configuration requirement corresponding to the physical disk addressing. If a selected component driver satisfies the physical disk addressing configuration requirement, then it would indicate that the requirement has been satisfied. If no component drivers so indicate during configuration of the device driver, the configuration requirement for physical disk addressing remains unsatisfied and access to the device related to the resulting device driver will not be granted to an application program.

FIG. 2 is a block diagram illustrating components of a computer system having device drivers configured during startup or restart in accordance with the present invention. As a result of this configuration, the computer system in FIG. 2 functions as follows. An application program 200 formulates Input/Output (I/O) requests and passes the requests to the operating system 201 through an application program interface 202. The application program interface 202 provides the application program 200 with access to the operating system 201. It should be noted that application programming interfaces are well known in the computer field, and are specific to the operating system associated therewith. When the application program interface 202 receives an I/O request, it invokes the input-output system (IOS), passing it the request.

The input-output system determines which device driver 204, 205 can service the request depending on which device 208, 209 is identified in the request. Device driver 204 comprises component drivers 210 and 211 through 212, and device driver 205 comprises component drivers 220 and 221 through 222. Within the device drivers, the component drivers 210 and 220 are the top layers and component drivers 212 and 222 are the bottom layers. Upon receiving the I/O request, if all configuration requirements have been satisfied in configuring the device driver for the requested device, the component drivers in the device driver are invoked and passed the I/O request. Initially, the input-output system invokes the top layer component driver, passing it the request. The top layer component driver performs component driver specific functions and invokes when appropriate the next lower layer component driver, passing it the request. The next lower layer component driver performs its own component driver specific functions and invokes when appropriate the next lower layer component driver, passing it the request, and so on. Finally, the bottom layer component driver interacts with the peripheral device, typically through a device adapter (not shown). Device adapters are well known in the computer field for interfacing between a computer system and a peripheral device.

FIG. 3 is a block diagram showing a sample disk drive device driver that is configured by the present invention. The disk drive device driver would be configured by the present invention as, for example, the device driver 204 if the device 208 were a disk drive. The disk drive device driver is implemented to perform synchronous I/O includes as component drivers which satisfy the configuration requirements of the disk drive, a data encryption component driver 301, a data compression component driver 302, and a disk component driver 303. The data encryption component driver encrypts or decrypts data and passes requests to the data compression component driver. The data compression component driver 302 works in an analogous manner to the data encryption component driver. That is, the data compression component driver compresses or decompresses data and passes the request along to the disk component driver. The disk component driver controls the reading and writing of the data to the disk drive through a disk drive adapter.

Upon receiving a write request to access the disk drive, for example, the IOS invokes the data encryption component driver, passing it the request to write data.

When requested to write data, the data encryption component driver encrypts the data and then invokes the data compression component driver, passing it the write request along with the encrypted data. The data compression component driver compresses the encrypted data and then invokes the disk component driver, passing it the write request along width the compressed data. In the case of the write request, the disk component driver 303 controls the disk drive to write the data to the disk. Upon completion, the component drivers each return control to the next higher layer component driver, and the top layer component driver returns to the IOS.

FIGS. 4, 5 and 6 illustrate the operation of the present invention once each device driver is configured to include the selected component drivers. Although configuration of device drivers will be described presently in detail with reference to FIGS. 7, 9, 11A and 11B, FIGS. 4, 5 and 6 and the discussion thereof are directed to execution of device drivers to process I/O requests, and based on the assumption that the device drivers have already been configure