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Device Driver Tutorial     Oracle Solaris 11.1 Information Library
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1.  Introduction to Device Drivers

Oracle Solaris Operating System Definition

Kernel Overview

Differences Between Kernel Modules and User Programs

Execution Differences Between Kernel Modules and User Programs

Structural Differences Between Kernel Modules and User Programs

Data Transfer Differences Between Kernel Modules and User Programs

User and Kernel Address Spaces on x86 and SPARC Machines

Device Drivers

Driver Directory Organization

Devices as Files

Devices Directories

Device Tree

Character and Block Devices

Device Names

Device Numbers

Development Environment and Tools

Writing a Driver

Writing a Driver Module

Writing a Configuration File

Building a Driver

Compiling with Oracle Solaris Studio

Compiling with the GNU C Compiler

Installing a Driver

Adding, Updating, and Removing a Driver

Loading and Unloading a Driver

Testing a Driver

2.  Template Driver Example

3.  Reading and Writing Data in Kernel Memory

4.  Tips for Developing Device Drivers


Development Environment and Tools

This section summarizes the driver development process and provides some pointers to resources. For more information on the development process, see Driver Development Summary in Writing Device Drivers.

Oracle offers training courses in Oracle Solaris OS internals, crash dump analysis, writing device drivers, DTrace, Oracle Solaris Studio, and other topics useful to Oracle Solaris developers. See for more information.

The general steps in writing a device driver are as follows:

  1. Write a .c source file using the interfaces and structures defined in man page sections 9E, 9F, and 9S. Most of the include files you need are in /usr/include/sys. The function and structure man pages show which include files you need.

  2. Write a .conf hardware configuration file to define property values for your driver.

  3. Compile and link your driver. Always use the -D_KERNEL option when you compile a driver for the Oracle Solaris OS. The default compile result is 32-bit. To get a 64-bit result on a 64-bit platform, specify the appropriate 64-bit option as described in Building a Driver.

  4. Copy your driver binary file and your driver configuration file to the appropriate [platform]/kernel directories. See Driver Directory Organization for descriptions of driver directories.

  5. Use the add_drv(1M) command to load your driver. When your driver is loaded, you can see your driver in /dev and /devices. You can also see an entry for your driver in the /etc/name_to_major file.

Writing a Driver

A driver consists of a C source file and a hardware configuration file.

Writing a Driver Module

The C code for a driver is a collection of data and functions that define a kernel module. As noted in Structural Differences Between Kernel Modules and User Programs, a driver has no main() routine. Many of the subroutines of a driver are special functions called entry points. See Device Drivers for information about entry points.

The function man pages provide both the function declaration that you need in your driver and the list of header files you need to include. Make sure you consult the correct man page. For example, the following command displays the ioctl(2) man page. The ioctl(2) system call cannot be used in a device driver.

% man ioctl

Use one of the following commands to display the ioctl(9E) man page. The ioctl(9E) subroutine is a device driver entry point.

% man ioctl.9e
% man -s 9e ioctl

By convention, the names of functions and data that are unique to this driver begin with a common prefix. The prefix is the name of this driver or an abbreviation of the name of this driver. Use the same prefix for all names that are specific to this driver. This practice makes debugging much easier. Instead of seeing an error related to an ambiguous attach() function, you see an error message about mydriver_attach() or newdriver_attach().

A 64-bit system can run both 32-bit user programs and 64-bit user programs. A 64-bit system runs 32-bit programs by converting all data needed between the two data models. A 64-bit kernel supports both 64-bit and 32-bit user data. Whenever a 64-bit driver copies data between kernel space and user space, the driver must use the ddi_model_convert_from(9F) function to determine whether the data must be converted between 32-bit and 64-bit models. For an example, see Reporting and Setting Device Size and Re-initializing the Device.

The Oracle Solaris Studio IDE includes the following three source editors: GVIM, XEmacs, and the built-in Source Editor provided by NetBeans. The IDE provides online help for these tools. You can also run GVIM and XEmacs from the command line. See vim(1) and xemacs(1).

For more information, see the following resources:

Writing a Configuration File

A driver that is not self-identifying might need a configuration file named node_name.conf, where node_name is the prefix for the device. A self-identifying driver is a driver that can obtain all the property information it needs from the DDI property interfaces such as ddi_prop_get_int(9F) and ddi_prop_lookup(9F). The minimum information that a configuration file must contain is the name of the device node and the name or type of the device's parent.

On the x86 platform, device information is supplied by the booting system. Hardware configuration files should no longer be needed, even for non-self-identifying devices.

For more information about device driver configuration files, see the driver.conf(4) man page. For an example configuration file, see Writing the Device Configuration File.

Building a Driver

This section tells you how to compile and link a driver for different architectures.

Make sure you have installed the Oracle Solaris OS at the Developer level or above.

A 64-bit kernel cannot use a 32-bit driver. A 64-bit kernel can use only 64-bit drivers. All parts of any particular program must use the same data model. A device driver is not a complete program. The kernel is a complete program. A driver is a part of the kernel program. If you want your device to work with the Oracle Solaris OS in 32-bit mode and in 64-bit mode, then you must provide both a 32-bit driver and a 64-bit driver.

By default, compilation on the operating system yields a 32-bit result on every architecture. To obtain a 64-bit result, use the compilation options specified in this section for 64-bit architectures.

Use the prtconf(1M) command with the -x option to determine whether the firmware on this system is 64-bit ready.

Compiling with Oracle Solaris Studio

Use the -D_KERNEL option to indicate that this code defines a kernel module.

Note - Sun Studio 9 does not support 64-bit x86 architectures. Use Sun Studio 10, Sun Studio 11, or Oracle Solaris Studio 12 to compile and debug drivers for 64-bit x86 architectures.

For more information on compile and link options, see the Oracle Solaris Studio 12.3 Command-line Reference and the Oracle Solaris Studio 12.2: C User’s Guide. To learn more about Oracle Solaris Studio, go to

Compiling with the GNU C Compiler

Use the -D_KERNEL option to indicate that this code defines a kernel module. These examples show options that are required for correct functionality of the result.

For more information on these and other options, see the gcc(1) man page. See also the GCC web site at

Installing a Driver

After you write and build your driver, you must install the driver binary. To install a driver, copy the driver binary and the configuration file to the appropriate /kernel/drv directory.

Make sure you are user root when you install a driver.

Copy the configuration file to the kernel driver area of the system.

# cp mydriver.conf /usr/kernel/drv

Install drivers in the /tmp directory until you are finished modifying and testing the _info(), _init(), and attach() routines. See Device Driver Testing Tips for more information.

Copy the driver binary to the /tmp directory.

# cp mydriver /tmp

Link to the driver from the kernel driver directory.

When the driver is well tested, copy the driver directly to the appropriate kernel driver area of the system.

Adding, Updating, and Removing a Driver

Use the add_drv(1M) command to make the installed driver usable. Be sure you are user root when you use the add_drv(1M) command.

# add_drv mydriver

The following events take place when you add a driver:

The file /etc/driver_aliases might be updated. The /etc/driver_aliases file shows which devices are bound to which drivers. If a driver is not listed in the /etc/driver_aliases file, then the OS does not load that driver or attach to that driver. Each line of the /etc/driver_aliases file shows a driver name followed by a device name. You can search this file to determine which driver is managing your device.

Note - Do not edit the /etc/driver_aliases file manually. Use the add_drv(1M) command to establish a device binding. Use the update_drv(1M) command to change a device binding.

The example drivers shown in this book manage pseudo devices. If your driver manages real hardware, then you need to use the -c and -i options on the add_drv(1M) command or the -i option on the update_drv(1M) command. To specify a device class or device ID, you might find the following sites useful. This information also is useful to search the /etc/driver_aliases file to find out whether a device already is supported.

Use the update_drv(1M) command to notify the system about attribute changes to an installed device driver. By default, the update_drv(1M) command reloads the hardware configuration file for the specified driver. Use the prtconf(1M) command to review the current configuration information for a device and driver. For example, the -D option shows which driver manages a particular device. The -P option shows information about pseudo devices.

Use the rem_drv(1M) command to update the system driver configuration files so that the driver is no longer usable. The rem_drv(1M) command does not physically delete driver files. If possible, the rem_drv(1M) command unloads the driver from memory.

Loading and Unloading a Driver

A driver is loaded into memory when a device that the driver manages is accessed. A driver might be unloaded from memory when the driver is not being used. Normally, you do not need to load a driver into memory manually or unload a driver from memory manually.

To manually load a loadable module into memory, use the modload(1M) command.

While you are developing your driver, you might want to manually unload the driver and then update the driver. To manually unload a loadable module from memory, use the modunload(1M) command.

Testing a Driver

Drivers should be thoroughly tested in the following areas:

For detailed information on how to test your driver and how to avoid problems during testing, see the following references:

Additional testing is specific to the type of driver.