Initiating the I/O operation

The following list outlines the steps involved when a peripheral driver initiates a read request. A similar process occurs for a write request.

Peripheral driver's read(D2osdi) routine

Create and populate a scsi_io_req(D4osdi) (also called REQ_IO or request block) structure to define the I/O operation. This structure defines various characteristics of the I/O operation, and points to the scsi_cdb(D4osdi) Command Descriptor Block (CDB) structure that tells the host adapter what operation is required.

Then call the host adapter's _entry(D2osdi) routine that is defined in the peripheral driver's scsi_dev_cfg(D4osdi) structure and block with the sleep(D3) function.

Host adapter's _entry(D2osdi) routine

extracts the scsi_cdb(D4osdi) (CDB or Command Descriptor Block) from the REQ_IO structure and initiates the appropriate I/O operation.