Other SAM Design Considerations

The SAM design considerations that are listed in this section must also be taken into account.

Responsibilities of the Device Driver
SAM device drivers are responsible for the following actions:
Options to the openx Subroutine
Device drivers must support eight defined extended options in their open routine.
Using the SC_FORCED_OPEN Option
The SC_FORCED_OPEN option forces access to a device by taking action to remove any type of reservation on the device that can inhibit access. The type of action to remove the reservation depends upon the specific type of the established reservation.
Using the SC_FORCED_OPEN_LUN Option
The SC_FORCED_OPEN_LUN option forces access to a device by taking action to remove any type of reservation on the device that can inhibit access.
Using the SC_RETAIN_RESERVATION Option
The SC_RETAIN_RESERVATION option causes the device driver to hold any established reservation as part of an open during the close of the device. For shared devices (for example, disk or CD-ROM), the device driver must OR together this option for all opens to a given device.
Using the SC_DIAGNOSTIC Option
The SC_DIAGNOSTIC option causes the device driver to enter Diagnostic mode for the given device. This option directs the device driver to perform only minimal operations to open a logical path to the device.
Using the SC_NO_RESERVE Option
The SC_NO_RESERVE option causes the device driver to prohibit any reservation commands during the open of the device. This facilitates the sharing of the device by multiple hosts.
Using the SC_SINGLE Option
The SC_SINGLE option causes the device driver to issue a normal open, but does not allow another caller to issue another open until the first caller has closed the device. This request gives the caller an exclusive open to the selected device.
Closing the Device
When a device driver is preparing to close a device through the adapter device driver, it must ensure that all transactions are complete.
Error Processing
It is the responsibility of the device driver to process check conditions and other returned errors properly.
Device Driver and Adapter Device Driver Interfaces
The device drivers can have both character (raw) and block special files in the /dev directory.
Performing Dumps
A device driver must have a dddump entry point if it drives a dump device.

Parent topic: SCSI Architectural Model Subsystem