Motorola MCP750 Specifications download pdf (Page 157)

Developing a Device Drive

10-11

Information needed to develop each type of driver I/O service routine is presented in the

sections that follow.

The Open Routine 10

Speciﬁcation

#include <sys/types.h>

#include <sys/file.h>

#include <sys/errno.h>

#include <sys/open.h>

#include <sys/cred.h>

#include <sys/ddi.h>

int xxopen (devp, oﬂag, otyp, crp)

dev_t devp;

int oﬂag;

int otyp;

cred_t *crp;

Return Values

• 0 if the device open is successful

• A nonzero value if the open fails. The number is returned to the user in

errno; it should be an error number as deﬁned in <sys/errno.h>.

The driver’s open entry point routine is called by the kernel during an open(2) of the

device special ﬁle. It is mandatory in all drivers.

The devp argument is a pointer to the device major and minor number.

The oflag argument is a flag that represents the file status flags set by the value of the

oflag argument set on the open(2) system call. The file status flags are defined in the

file <sys/file.h>.

The following bits are set if the corresponding bits are set on the open(2) system call:

FREAD Open the device with read access permission

FWRITE Open the device with write access permission

FNDELAY Open the device and return immediately without sleeping

(do not block the open even if there is a problem). On a read

or a write, 0 is returned if the request cannot be satisfied

immediately.

FNONBLOCK Open the device and return immediately without sleeping

(do not block the open even if there is a problem). On a read

or a write, -1 is returned, and errno is set to EAGAIN if

the request cannot be satisﬁed immediately.

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Motorola MCP750 Specifications Page 157