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man pages section 9: DDI and DKI Driver Entry Points

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Updated: Friday, August 13, 2021



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);

Interface Level

Solaris DDI specific (Solaris DDI)



Pointer to a kstat(9S) structure.


Read/Write flag. Possible values are


Update kstat structure statistics from the driver.


Update driver statistics from the kstat structure.


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 the kstat_install() function. For more information, see the kstat_install(9F) man page.

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


For success.


If KSTAT_WRITE is not allowed.


For any other error.

See Also

kstat_create(9F), kstat_install(9F), kstat(9S), kstat2_create(9F), kstat2_install(9F), kstat2(9S)

Writing Device Drivers in Oracle Solaris 11.4


The ks_update() function is deprecated. Use the kstat2_create() to create a kstat and set the ks2_update field to point to the update function. For more information, see the kstat2_create(9F) man page.