NAME

read - read data from a device

SYNOPSIS

#include <sys/types.h>

#include <sys/errno.h>
#include <sys/open.h>
#include <sys/uio.h>
#include <sys/cred.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>

int prefixread(dev_t dev, struct uio * uio_p, cred_t * cred_p);

INTERFACE LEVEL

Architecture independent level 1 (DDI/DKI). This entry point is optional.

ARGUMENTS

dev

Device number.

uio_p

Pointer to the uio (9S)structure that describes where the data is to be stored in user space.

cred_p

Pointer to the user credential structure for the I/O transaction.

DESCRIPTION

The driver read( ) routine is called indirectly through cb_ops(9S) by the read (2)system call. The read( ) routine should check the validity of the minor number component of dev and the user credential structure pointed to by cred_p (if pertinent). The read( ) routine should supervise the data transfer into the user space described by the uio (9S)structure.

RETURN VALUES

The read( ) routine should return 0 for success, or the appropriate error number.

EXAMPLES

The following is an example of a read( ) routine using physio(9F) to perform reads from a non-seekable device:

static int
xxread(dev_t dev, struct uio * uiop,cred_t * credp)
{
           int                         rval;
           offset_t                    off;
           int                         instance;
           xx_t                        xx;

instance = getminor(dev);

xx = ddi_get_soft_state(xxstate, instance);
if (xx == NULL)
           return (ENXIO);
off = uiop->uio_loffset;
rval = physio(xxstrategy, NULL, dev, B_READ,
           xxmin, uiop);
uiop->uio_loffset = off;

           return (rval);
}

SEE ALSO

read (2),write(9E), physio(9F), cb_ops(9S), uio (9S)

Writing Device Drivers