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

illumos DDI specific (illumos 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 consistent
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


May 27, 1994 KS_UPDATE(9E)