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Driver Loading

When a service requires the use of your driver, Open Transport will automatically load it and install it into the STREAMS module tables. In order to do this, your module must export a function named either GetOTInstallInfo or GetOT xxxxx InstallInfo (where xxxxx is the name of the module or driver).

This function returns the installation information that Open Transport needs to install the driver into the STREAMS tables, using the following data structure:

install_str

This is a pointer to the driver's streamtab structure.

install_flags

This contains flags to inform Open Transport of your driver's STREAMS module type. The install_flags should be set to kOTModIsDriver | kOTModIsPortDriver for STREAMS port drivers.

install_sqlvl

This flag is set to the type of reentrancy your driver can handle. Possible values are the following:

SQLVL_QUEUE	The driver can be entered once from the upper queue and once from the lower queue at the same time.
SQLVL_QUEUEPAIR	The driver can be entered from either the upper queue or the lower queue, but not at the same time.
SQLVL_MODULE	The driver can be entered only once per port, regardless of which instance of the module is entered.
SQLVL_GLOBAL	Among all modules that use SQLVL_GLOBAL only one will be entered at a time.

install_buddy

This field is currently not support by Open Transport. It should be set to NULL.

ref_load

This field keeps a load reference to the driver. It should be initialized to 0 and then never touched.

ref_count

This field monitors when a driver is first loaded and last unloaded. It should be initialized to 0 and then never touched.

Whenever Open Transport loads your module or driver, and the ref_count field of the install_info structure is 0, Open Transport will call an optional initialization function exported by the module. This function must be named either InitStreamModule or Init xxxxx StreamModule (where xxxxx is the name of the module or driver).

If InitStreamModule returns false to Open Transport, then the loading of the module will be aborted and an ENXIO error will be returned to the client. Otherwise, the module will be loaded and installed into a stream.

The systemDependent parameter is a pointer to the cookie value used when registering the port. For drivers loaded using the System registry, its value is RegEntryIDPtr.

If the PCI device supports changing power levels, the InitStreamModule function should set the power level for normal operation.

Whenever Open Transport removes the last instance of a module or driver from the system, it calls an optional termination function exported by the module. This function must be named either TerminateStreamModule or Terminate xxxxx StreamModule (where xxxxx is the name of the module or driver).

If the PCI device supports changing power levels, the TerminateStreamModule function should set the power level to low power or no power, as appropriate.

Of course, modules and drivers may also use the initialization and termination features of their DLL technology. Both CFM and ASLM allow initialization and termination routines. However, only a call to InitStreamModule implies that the module is about to be loaded into a stream. Open Transport often loads a module just to call the GetOTInstallInfo information.

All memory allocations that do not use the Open Transport allocation routines ( OTAllocMem and OTFreeMem ) or any interrupt-safe allocators supplied by the interrupt subsystem must be performed from within the initialization and termination routines--that is, PoolAllocateResident and PoolDeallocate may be called only from them.

Once your port driver has been loaded, all communication with it will be through STREAMS messages and the entry points in the streamtab.