Tribblix: manual page: read.9e

READ(9E) Driver Entry Points READ(9E)

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.

PARAMETERS

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

Example 1 read() routine using physio()

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);
}