Motorola MCP750 Specifications download pdf (Page 162)

evice Driver Programming

10-16

The Write Routine 10

Speciﬁcation

#include <sys/types.h>

#include <sys/errno.h>

#include <sys/uio.h>

#include <sys/cred.h>

#include <sys/ddi.h>

int xxwrite (dev, uio_p, crp)

dev_t dev;

uio_t *uio_p;

cred_t *crp;

Return Values

• 0 if the device write is successful

• A nonzero value if the write 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 write(D2) routine is called when the write(2) system call is made to

write data to the device. This entry point is optional.

The dev argument specifies the device major and minor number.

The uio_p argument is a pointer to a uio structure that describes the location and layout of

the user’s I/0 buffers. This structure is defined in <sys/uio.h>; it is described in sec-

tion Chapter 9, “The iovec and uio Structures” on page 9-7.

NOTE

A driver compiled as a large offset driver is passed (and expects to

get) the large offset version of the uio structure for the

write(D2) interface it supplies. The same applies for small off-

set drivers. For details on how this is done, see Chapter 9, the sec-

tion “Small vs. Large Offset Drivers” on page 9-21.

The crp argument is a pointer to the cred structure associated with the user process.

The uio structure contains the number and position of the characters as given by the user.

uio–>uio_resid is the number of characters in the uio structure. The uio structure

contains a pointer to an array of iovec structures in uio->uio_iov. The number of iovec

structures is kept in uio->uio_iovcnt. Each iovec structure contains the base address of

the user’s characters in iovec->iov_base and the number of characters in iovec->iov_len.

The system can call the routine internally, so the flag uio->uio_segflg is supplied that

determines if the iovec structures refer to the system address space instead of the user’s.

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Motorola MCP750 Specifications Page 162