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);


      }