STREAMS-UX Programmer's Guide (February 2007)

Modules and Drivers

Entry Points

Chapter 4

Entry Points

This section explains the entry points for drivers and modules in detail.

Open

The open routine for a driver is called when the device is first opened by the user process with an open (2)

system call. The module open routine is called when the module is pushed onto the stream with I_PUSH

IOCTL command or with the autopush utility.

For SVR 4 compliance, the open routine has the following definition:

int drv_open(queue_t *q, dev_t *devp, int oflag, int sflag, cred_t *credp);

For SVR 3.2 compliance, the open routine is as follows:

int drv_open(queue_t *q, dev_t devp, int oflag, int sflag, cred_t *credp);

q is the pointer to the driver/module’s read queue. devp points to the device pointer in SVR4 open (2). devp is

the device number in SVR 3.2 open (2). oflag are the flags used by the application in the open (2) system

call, sflag indicates the type of STREAMS open to perform and credp point to the processes credentials. On

success the open routine should return 0 and an error number on failure.

Valid sflag values are defined in <sys/stream.h> and are as follows:

0 — Non-cloneable driver open

CLONEOPEN — Cloneable driver open

MODOPEN — Module open

Do not call a driver with the sflag set to MODOPEN. But, as a driver can be configured as both module and

driver, appropriate sflag should be used in the open routine. i.e., when it is configured as driver sflag

should be set to 0 or CLONEOPEN and when it is configured as module sflag should be set to MODOPEN.

In the open routine the module or driver allocates and initializes its resources. For same minor device, the

driver open routines are serialized and only one open routine will be allowed to process at a time. Usually, the

first open of the device will allocate the structures and subsequent open routines will have very little

processing to do if any. Modules and drivers can sleep in the open routine at an uninterruptible priority level

or with PCATCH set, as it has user context.

The close routine for a driver is invoked on the last close of the device. The close routine for a module is

invoked when it is popped from the stream as a result of a I_POP IOCTL command or closing of the stream.

For SVR 4 compliance, the close routine has the following definition:

int drv_close(queue_t *q, int oflag, cred_t *credp);

For the SVR 3.2 compliance, the close routine is as follows:

int drv_close(queue_t *q, int oflag);

Where q is the pointer to the driver or modules read queue, oflag is the bitmask of flags indicating the file

status and credp point to the processes credentials. On success the close routine should return 0 and it

returns an error value on failure, even though the return value from the close routine is currently ignored by

STREAMS.