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 valid-
       ity 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);
	       }

SEE ALSO

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

       Writing Device Drivers

SunOS 5.11							    19 Nov 1997 							  read(9E)