INTRO(9E) Driver Entry Points INTRO(9E)

Intro, intro - overview of device driver interfaces and introduction to driver entry points

This page provides an overview of device driver interfaces and all of the Section 9 man pages (9E, 9F, 9P, and 9S). This overview is followed by an introduction to Section 9E, the driver entry-point routines.

Section 9 provides reference information needed to write device drivers for the illumos operating system. It describes the interfaces provided by the Device Driver Interface and the Driver-Kernel Interface (DDI/DKI).

Software is usually considered portable if it can be adapted to run in a different environment more cheaply than it can be rewritten. The new environment may include a different processor, operating system, and even the language in which the program is written, if a language translator is available. Likewise the new environment might include multiple processors. More often, however, software is ported between environments that share an operating system, processor, and source language. The source code is modified to accommodate the differences in compilers or processors or releases of the operating system.

In the past, device drivers did not port easily for one or more of the following reasons:

To enhance functionality, members had been added to kernel data structures accessed by drivers, or the sizes of existing members had been redefined.
The calling or return syntax of kernel functions had changed.
Driver developers did not use existing kernel functions where available, or relied on undocumented side effects that were not maintained in the next release.
Architecture-specific code had been scattered throughout the driver when it could have been isolated.

Operating systems are periodically reissued to customers as a way to improve performance, fix bugs, and add new features. This is probably the most common threat to compatibility encountered by developers responsible for maintaining software. Another common problem is upgrading hardware. As new hardware is developed, customers occasionally decide to upgrade to faster, more capable computers of the same family. Although they may run the same operating system as those being replaced, architecture-specific code may prevent the software from porting.

Although application programs have all of the porting problems mentioned, developers attempting to port device drivers have special challenges. Before describing the DDI/DKI, it is necessary to understand the position of device drivers in operating systems.

Device drivers are kernel modules that control data transferred to and received from peripheral devices but are developed independently from the rest of the kernel. If the goal of achieving complete freedom in modifying the kernel is to be reconciled with the goal of binary compatibility with existing drivers, the interaction between drivers and the kernel must be rigorously regulated. This driver/kernel service interface is the most important of the three distinguishable interfaces for a driver, summarized as follows:

Driver-Kernel. I/O System calls result in calls to driver entry point routines. These make up the kernel-to-driver part of the service interface, described in Section 9E. Drivers may call any of the functions described in Section 9F. These are the driver-to-kernel part of the interface.
Driver-Hardware. All drivers (except software drivers) must include code for interrupt handling, and may also perform direct memory access (DMA). These and other hardware-specific interactions make up the driver/hardware interface.
Driver-Boot/Configuration Software. The interaction between the driver and the boot and configuration software is the third interface affecting drivers.

The primary goal of the DDI/DKI is to facilitate both source and binary portability across successive releases of the operating systems on a particular machine. In addition, it promotes source portability across implementations of UNIX on different machines, and applies only to implementations based on System V Release 4. The DDI/DKI consists of several sections:
DDI/DKI Architecture Independent - These interfaces are supported on all implementations of System V Release 4.
DKI-only - These interfaces are part of System V Release 4, and may not be supported in future releases of System V. There are only two interfaces in this class, segmap(9E) and hat_getkpfnum(9F)
illumos DDI - These interfaces specific to illumos.
illumos SPARC specific DDI - These interfaces are specific to the SPARC processor, and may not be available on other processors supported by illumos.
illumos x86 specific DDI - These interfaces are specific to the x86 processor, and may not be available on other processors supported by illumos.

To achieve the goal of source and binary compatibility, the functions, routines, and structures specified in the DDI/DKI must be used according to these rules.

Drivers cannot access system state structures (for example, u and sysinfo) directly.
For structures external to the driver that may be accessed directly, only the utility functions provided in Section 9F should be used. More generally, these functions should be used wherever possible.
The headers <sys/ddi.h> and <sys/sunddi.h> must be the last header files included by the driver.

Section 9 is for software engineers responsible for creating, modifying, or maintaining drivers that run on this operating system and beyond. It assumes that the reader is familiar with system internals and the C programming language.

The PC Card 95 Standard is listed under the SEE ALSO heading in some Section 9 reference pages. This refers to documentation published by the Personal Computer Memory Card International Association (PCMCIA) and the Japan Electronic Industry Development Association (JEIDA).

Section 9 is divided into the following subsections:


Driver Entry Points - contains reference pages for all driver entry point routines.


Kernel Functions - contains reference pages for all driver support routines.


Driver Properties - contains reference pages for driver properties.


Data Structures - contains reference pages for driver-related structures.

Sun Microsystem's implementation of the DDI/DKI was designed to provide binary compatibility for third-party device drivers across currently supported hardware platforms across minor releases of the operating system. However, unforeseen technical issues may force changes to the binary interface of the DDI/DKI. We cannot therefore promise or in any way assure that DDI/DKI-compliant device drivers will continue to operate correctly on future releases.

Section 9E describes the entry-point routines a developer can include in a device driver. These are called entry-point because they provide the calling and return syntax from the kernel into the driver. Entry-points are called, for instance, in response to system calls, when the driver is loaded, or in response to STREAMS events.

Kernel functions usable by the driver are described in section 9F.

In this section, reference pages contain the following headings:

NAME describes the routine's purpose.
SYNOPSIS summarizes the routine's calling and return syntax.
INTERFACE LEVEL describes any architecture dependencies. It also indicates whether the use of the entry point is required, optional, or discouraged.
ARGUMENTS describes each of the routine's arguments.
DESCRIPTION provides general information about the routine.
RETURN VALUES describes each of the routine's return values.
SEE ALSO gives sources for further information.

By convention, a prefix string is added to the driver routine names. For a driver with the prefix prefix, the driver code may contain routines named prefixopen, prefixclose, prefixread, prefixwrite, and so forth. All global variables associated with the driver should also use the same prefix.

All routines and data should be declared as static.

Every driver MUST include <sys/ddi.h> and <sys/sunddi.h>, in that order, and after all other include files.

The following table summarizes the STREAMS driver entry points described in this section.

Routine Type

The following table summarizes the driver entry points described in this section.

Routine Type
_fini illumos DDI
_info illumos DDI
_init illumos DDI
aread illumos DDI
attach illumos DDI
awrite illumos DDI
chpoll DDI/DKI
close DDI/DKI
detach illumos DDI
devmap illumos DDI
devmap_access illumos DDI
devmap_contextmgt illumos DDI
devmap_dup illumos DDI
devmap_map illumos DDI
devmap_unmap illumos DDI
dump illumos DDI
getinfo illumos DDI
identify illumos DDI
ioctl DDI/DKI
ks_update illumos DDI
mapdev_access illumos DDI
mapdev_dup illumos DDI
mapdev_free illumos DDI
mmap DKI only
open DDI/DKI
power illumos DDI
print DDI/DKI
probe illumos DDI
prop_op illumos DDI
read DDI/DKI
segmap DKI only
strategy DDI/DKI
tran_abort illumos DDI
tran_destroy_pkt illumos DDI
tran_dmafree illumos DDI
tran_getcap illumos DDI
tran_init_pkt illumos DDI
tran_reset illumos DDI
tran_reset_notify illumos DDI
tran_setcap illumos DDI
tran_start illumos DDI
tran_sync_pkt illumos DDI
tran_tgt_free illumos DDI
tran_tgt_init illumos DDI
tran_tgt_probe illumos DDI
write DDI/DKI

The following table lists the error codes returned by a driver routine when it encounters an error. The error values are listed in alphabetic order and are defined in sys/errno.h. In the driver open(9E), close(9E), ioctl(9E), read(9E), and write(9E) routines, errors are passed back to the user by calling bioerror(9F) to set b_flags to the proper error code. In the driver strategy(9E) routine, errors are passed back to the user by setting the b_error member of the buf(9S) structure to the error code. For STREAMS ioctl routines, errors should be sent upstream in an M_IOCNAK message. For STREAMS read() and write() routines, errors should be sent upstream in an M_ERROR message. The driver print routine should not return an error code because the function that it calls, cmn_err(9F), is declared as void (no error is returned).

Error Value Error Description
EAGAIN Kernel resources, such as the buf structure or cache memory, are not available at this time (device may be busy, or the system resource is not available). This is used in open, ioctl, read, write, and strategy.
EFAULT An invalid address has been passed as an argument; memory addressing error. This is used in open, close, ioctl, read, write, and strategy.
EINTR Sleep interrupted by signal. This is used in open, close, ioctl, read, write, and strategy.
EINVAL An invalid argument was passed to the routine. This is used in open, ioctl, read, write, and strategy.
EIO A device error occurred; an error condition was detected in a device status register (the I/O request was valid, but an error occurred on the device). This is used in open, close, ioctl, read, write, and strategy.
ENXIO An attempt was made to access a device or subdevice that does not exist (one that is not configured); an attempt was made to perform an invalid I/O operation; an incorrect minor number was specified. This is used in open, close, ioctl, read, write, and strategy.
EPERM A process attempting an operation did not have required permission. This is used in open, ioctl, read, write, and strategy.
EROFS An attempt was made to open for writing a read-only device. This is used in open.

The table below cross references error values to the driver routines from which the error values can be returned.

open close ioctl read, write and strategy

Intro(9F), Intro(9S)
May 15, 2001 OmniOS