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|Writing Device Drivers Oracle Solaris 11.1 Information Library|
This section provides lists of entry points for the following categories:
Some operations can be performed by any type of driver, such as the functions that are required for module loading and for the required autoconfiguration entry points. This section discusses types of entry points that are common to all drivers. The common entry points are listed in Summary of Common Entry Points with links to man pages and other relevant discussions.
Drivers for character and block devices export the cb_ops(9S) structure, which defines the driver entry points for block device access and character device access. Both types of drivers are required to support the open(9E) and close(9E) entry points. Block drivers are required to support strategy(9E), while character drivers can choose to implement whatever mix of read(9E), write(9E), ioctl(9E), mmap(9E), or devmap(9E) entry points is appropriate for the type of device. Character drivers can also support a polling interface through chpoll(9E). Asynchronous I/O is supported through aread(9E) and awrite(9E) for block drivers and those drivers that can use both block and character file systems.
Note - In the Oracle Solaris OS, only the loadable module routines must be visible outside the driver object module. Other routines can have the storage class static.
Drivers are required to implement the attach(9E), detach(9E), and getinfo(9E) entry points for device autoconfiguration. Drivers can also implement the optional entry point probe(9E) in cases where devices do not identify themselves during boot-up, such as SCSI target devices. See Chapter 6, Driver Autoconfiguration for more information on these routines.
The Oracle Solaris platform provides a rich set of interfaces to maintain and export kernel-level statistics, also known as kstats. Drivers are free to use these interfaces to export driver and device statistics that can be used by user applications to observe the internal state of the driver. Two entry points are provided for working with kernel statistics:
ks_snapshot(9E) captures kstats at a specific time.
ks_update(9E) can be used to update kstat data at will. ks_update() is useful in situations where a device is set up to track kernel data but extracting that data is time-consuming.
A driver that manages devices must implement the quiesce(9E) entry point. Drivers that do not manage devices can set the devo_quiesce field in the dev_ops structure to ddi_quiesce_not_needed(). The quiesce() function can be called only when the system is single-threaded at high PIL (priority interrupt level) with preemption disabled. Therefore, this function must not be blocked. If a device has a defined reset state configuration, the driver should return that device to that reset state as part of the quiesce operation. An example of this case is Fast Reboot, where firmware is bypassed when booting to a new operating system image.
The following table lists entry points that can be used by all types of drivers.
Table 1-1 Entry Points for All Driver Types
Devices that support a file system are known as block devices. Drivers written for these devices are known as block device drivers. Block device drivers take a file system request, in the form of a buf(9S) structure, and issue the I/O operations to the disk to transfer the specified block. The main interface to the file system is the strategy(9E) routine. See Chapter 16, Drivers for Block Devices for more information.
A block device driver can also provide a character driver interface to enable utility programs to bypass the file system and to access the device directly. This device access is commonly referred to as the raw interface to a block device.
The following table lists additional entry points that can be used by block device drivers. See also Entry Points Common to All Drivers.
Table 1-2 Additional Entry Points for Block Drivers
Character device drivers normally perform I/O in a byte stream. Examples of devices that use character drivers include tape drives and serial ports. Character device drivers can also provide additional interfaces not present in block drivers, such as I/O control (ioctl) commands, memory mapping, and device polling. See Chapter 15, Drivers for Character Devices for more information.
The main task of any device driver is to perform I/O, and many character device drivers do what is called byte-stream or character I/O. The driver transfers data to and from the device without using a specific device address. This type of transfer is in contrast to block device drivers, where part of the file system request identifies a specific location on the device.
The following table lists additional entry points that can be used by character device drivers. For other entry points, see Entry Points Common to All Drivers.
Table 1-3 Additional Entry Points for Character Drivers
STREAMS is a separate programming model for writing a character driver. Devices that receive data asynchronously, such as terminal and network devices, are suited to a STREAMS implementation. STREAMS device drivers must provide the loading and autoconfiguration support described in Chapter 6, Driver Autoconfiguration. See the STREAMS Programming Guide for additional information on how to write STREAMS drivers.
The following table lists additional entry points that can be used by STREAMS device drivers. For other entry points, see Entry Points Common to All Drivers and Entry Points for Character Device Drivers.
Table 1-4 Entry Points for STREAMS Drivers
For certain devices, such as frame buffers, providing application programs with direct access to device memory is more efficient than byte-stream I/O. Applications can map device memory into their address spaces using the mmap(2) system call. To support memory mapping, device drivers implement segmap(9E) and devmap(9E) entry points. For information on devmap(9E), see Chapter 10, Mapping Device and Kernel Memory. For information on segmap(9E), see Chapter 15, Drivers for Character Devices.
The following table lists additional entry points that can be used by character device drivers that use the devmap framework to perform memory mapping. For other entry points, see Entry Points Common to All Drivers and Entry Points for Character Device Drivers.
Table 1-5 Entry Points for Character Drivers That Use devmap for Memory Mapping
See Table 19-1 for a list of entry points for network device drivers that use the Generic LAN Driver version 3 (GLDv3) framework. For more information, see GLDv3 Network Device Driver Framework and GLDv3 MAC Registration Functions in Chapter 19, Drivers for Network Devices.
The following table lists additional entry points that can be used by SCSI HBA device drivers. For information on the SCSI HBA transport structure, see scsi_hba_tran(9S). For other entry points, see Entry Points Common to All Drivers and Entry Points for Character Device Drivers.
Table 1-6 Additional Entry Points for SCSI HBA Drivers
The following table lists additional entry points that can be used by PC Card device drivers. For other entry points, see Entry Points Common to All Drivers and Entry Points for Character Device Drivers.
Table 1-7 Entry Points for PC Card Drivers Only