Writing a SCSI peripheral driver

This chapter uses ``xx_'' to represent the SCSI peripheral driver's prefix. Your driver should replace ``xx_'' with the prefix defined for your driver.

The routines discussed are:

• ``xxinit and xxinit2'' registers the device and initializes data structures required for the SCSI peripheral driver.

• ``open'' checks errors and permissions and completes initialization for the peripheral.

• ``read and write'' call the xxstrategy routine directly or through the kernel's physio(K) routine.

• ``strategy'' builds and queues a request by sending it to the host adapter driver via the configured xx_entry routine, taking care to check for possible errors. This request contains a pointer to an interrupt handler routine to call at interrupt time.

• ``intr'' At interrupt time, the SCSI host adapter driver handles the interrupt, determines the SCSI peripheral that caused the interrupt, and passes the interrupt along with appropriate data structure pointers to the SCSI peripheral driver's intr(D2osdi) routine, also called the callback function. This routine then processes the information and passes it back to the calling user process.

SCSI peripheral drivers must use the standard structures required by the kernel for that type of device. ``Notes about drivers for disk devices'' provides notes about the requirements for disk devices.