ks_update(9E)							Driver Entry Points						     ks_update(9E)

NAME

       ks_update - dynamically update kstats

SYNOPSIS

       #include <sys/types.h>
       #include <sys/kstat.h>
       #include <sys/ddi.h>
       #include <sys/sunddi.h>

       int prefix_ks_update(kstat_t *ksp, int rw);

INTERFACE LEVEL

       Solaris DDI specific (Solaris DDI)

PARAMETERS

       ksp     Pointer to a kstat(9S) structure.

       rw      Read/Write flag. Possible values are

	       KSTAT_READ      Update kstat structure statistics from the driver.

	       KSTAT_WRITE     Update driver statistics from the kstat structure.

DESCRIPTION

       The  kstat  mechanism  allows  for  an optional ks_update() function to update kstat data.  This is useful for drivers where the underlying
       device keeps cheap hardware statistics, but extraction is expensive.  Instead of constantly keeping the kstat data section up to date,  the
       driver  can  supply  a  ks_update()  function  which updates the kstat's data section on demand. To take advantage of this feature, set the
       ks_update field before calling kstat_install(9F).

       The ks_update() function must have the following structure:

	 static int
	 xx_kstat_update(kstat_t *ksp, int rw)
	 {
	      if (rw == KSTAT_WRITE) {
		   /* update the native stats from ksp->ks_data */
		   /* return EACCES if you don't support this */
	      } else {
		   /* update ksp->ks_data from the native stats */
	      }
	      return(0);
	 }

       In general, the ks_update() routine may need to refer to provider-private data; for example, it may need a pointer to  the  provider's  raw
       statistics.  The ks_private field is available for this purpose.   Its use is entirely at the provider's discretion.

       No kstat locking should be done inside the ks_update() routine.	The caller will already be holding the kstat's	ks_lock (to ensure consis-
       tent data) and will prevent the kstat from being removed.

RETURN VALUES

       ks_update() should return

       0	  For success.

       EACCES	  If KSTAT_WRITE is not allowed.

       EIO	  For any other error.

SEE ALSO

       kstat_create(9F), kstat_install(9F), kstat(9S)

       Writing Device Drivers

SunOS 5.11							    27 May 1994 						     ks_update(9E)