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);
           }

SEE ALSO

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

     Writing Device Drivers