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ks_update - dynamically update kstats

#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);

illumos DDI specific (illumos DDI) ksp rw 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.

ks_update() should return 0 EACCES EIO kstat_create(9F), kstat_install(9F), kstat(9S)

Writing Device Drivers