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)