Driver Entry Points                                     aread(9E)



NAME
     aread - asynchronous read from a device

SYNOPSIS
     #include 
     #include 
     #include 
     #include 
     #include 
     intprefix

     aread(devt dev, struct aioreq *aioreqp, credt *credp);


INTERFACE LEVEL
     Solaris DI specific (Solaris  DI).  This  entry  point  is
     optional. Drivers that do not support an aread() entry point
     should use nodev(9F)

PARAMETERS
     dev          Device number.


     aioreqp     Pointer  to  the  aioreq(9S)  structure   that
                  describes where the data is to be stored.


     credp       Pointer to the credential structure.


DESCRIPTION
     The driver's aread() routine is called to perform  an  asyn-
     chronous  read. getminor(9F) can be used to access the minor
     number component of the dev argument. aread()  may  use  the
     credential  structure  pointed  to  by  credp  to check for
     superuser access by calling drvpriv(9F). The  aread()  rou-
     tine  may  also  examine  the  uio(9S) structure through the
     aioreq  structure  pointer,  aioreqp.  aread()  must  call
     aphysio(9F)  with  the  aioreq pointer and a pointer to the
     driver's strategy(9E) routine.


     No fields of the uio(9S) structure pointed  to  by  aioreq,
     other  than  uiooffset  or uioloffset, may be modified for
     non-seekable devices.

RETURN VALUES
     The aread() routine should return  0  for  success,  or  the
     appropriate error number.

CONTEXT




SunOS 5.11          Last change: 28 Mar 1997                    1






Driver Entry Points                                     aread(9E)



     This function is called from user context only.

EXAMPLES
     Example 1 The following is an example of an aread() routine:

       static int
       xxaread(devt dev, struct aioreq *aio, credt *credp)
       {
            int instance;
            struct xxstate *xsp;
            instance = getminor(dev);
            xsp = ddigetsoftstate(statep, instance);
            /*Verify soft state structure has been allocated */
            if (xsp == NUL)
                 return (ENXIO);
            return (aphysio(xxstrategy, anocancel,
                                dev, BREAD, xxminphys, aio));
       }


SEE ALSO
     read(2), aioread(3C),  awrite(9E),  read(9E),  strategy(9E),
     write(9E),            anocancel(9F),            aphysio(9F),
     ddigetsoftstate(9F),     drvpriv(9F),      getminor(9F),
     minphys(9F), nodev(9F), aioreq(9S), cbops(9S), uio(9S)


     Writing Device Drivers

BUGS
     There is no way other than calling aphysio(9F) to accomplish
     an asynchronous read.























SunOS 5.11          Last change: 28 Mar 1997                    2