Opens a communication session on a channel opened by a ddopen entry point.
| Item | Description |
|---|---|
| devno | Specifies major and minor device numbers. |
| op | Specifies the entry point for the CIO_START operation. |
| parmptr | Points to a session_blk structure. This structure is defined in the /usr/include/sys/comio.h file. |
| devflag | Specifies the DKERNEL flag. This flag is set by calling kernel-mode processes and cleared by calling user-mode processes. |
| chan | Specifies the channel number assigned by the device handler's ddmpx entry point. |
| ext | Indicates device-dependent. |
The CIO_START operation must be supported by each physical device handler (PDH) in the communication I/O subsystem. Its use varies from adapter to adapter. This operation opens a communication session on a channel opened by a ddopen entry point. Once a channel is opened, multiple CIO_START operations can be issued. For each successful start, a corresponding CIO_HALT operation must be issued later.
The CIO_START operation requires only the netid input parameter. This parameter is registered for the session. At least one network ID must be registered for this session before the PDH successfully accepts a call to the ddwrite or ddread entry point on this session. If this start is the first issued for this port or adapter, the appropriate hardware initialization is performed. Time-consuming initialization activities, such as call connection, are also performed.
This call returns immediately to the caller before the asynchronous command completes. If the return indicates no error, the PDH builds a CIO_START_DONE status block upon completion. For kernel-mode processes, the status block is passed to the associated status function (specified at open time). For user-mode processes, the status block is placed in the associated status or exception queue.
The session_blk Parameter Block
For the CIO_START operation, the ext parameter may be a pointer to a session_blk structure. This structure is defined in the /usr/include/sys/comio.h file and contains the following fields:
| Field | Description |
|---|---|
| status | Indicates the status of the port. This field may contain
additional information about the completion of the CIO_START operation.
Besides the status codes listed here, device-dependent codes can also
be returned:
|
| netid | Contains the network ID to register with the start. |
A CIO_START operation can be called from the process environment only.
In general, communication device-handlers use the common return codes defined for an entry point. However, device handlers for specific communication devices may return device-specific codes. The common return codes for the CIO_START operation are the following:
| Return Code | Description |
|---|---|
| ENXIO | Indicates an attempt to use an unconfigured device. |
| EFAULT | Indicates a specified address is not valid. |
| EINVAL | Indicates a parameter is not valid. |
| ENOSPC | Indicates the network ID table is full. |
| EADDRINUSE | Indicates a duplicate network ID. |
| EBUSY | Indicates the maximum number of opens was exceeded. |
| ENODEV | Indicates the device does not exist. |