READ(9E)READ(9E)NAMEread - 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 trans‐
action.
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 super‐
vise 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);
}
SEE ALSOread(2), write(9E), physio(9F), cb_ops(9S), uio(9S)
Writing Device Drivers
Nov 19, 1997 READ(9E)
