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man pages section 9: DDI and DKI Driver Entry Points

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Updated: July 2017



ks_snapshot - take a snapshot of kstat data


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

int prefix_ks_snapshot(kstat_t *ksp, void *buf, int rw);

Interface Level

Solaris DDI specific (Solaris DDI).



Pointer to a kstat(9S) structure.


Pointer to a buffer to copy the snapshot into.


Read/Write flag. Possible values are:


Copy driver statistics from the driver to the buffer.


Copy statistics from the buffer to the driver.


The kstat mechanism allows for an optional ks_snapshot() function to copy kstat data. This is the routine that is called to marshall the kstat data to be copied to user-land. A driver can opt to use a custom snapshot routine rather than the default snapshot routine; to take advantage of this feature, set the ks_snapshot field before calling kstat_install(9F).

The ks_snapshot() function must have the following structure:

static int
xx_kstat_snapshot(kstat_t *ksp, void *buf, int rw)
     if (rw == KSTAT_WRITE) {
/* set the native stats to the values in buf */
/* return EACCES if you don't support this */
     } else {
/* copy the kstat-specific data into buf */
     return (0);

In general, the ks_snapshot() routine might need to refer to provider-private data; for example, it might 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.

  1. ks_snaptime must be set (via gethrtime(9F)) to timestamp the data.

  2. Data gets copied from the kstat to the buffer on KSTAT_READ, and from the buffer to the kstat on KSTAT_WRITE.

Return Values




If KSTAT_WRITE is not allowed


For any other error


This function is called from user context only.


Example 1 Named kstats with Long Strings (KSTAT_DATA_STRING)
static int
xxx_kstat_snapshot(kstat_t *ksp, void *buf, int rw)
    if (rw == KSTAT_WRITE) {
         return (EACCES);
    } else {
         kstat_named_t *knp = buf;
         char *end = knp + ksp->ks_ndata;
         uint_t i;

         bcopy(ksp->ks_data, buf,
                 sizeof (kstat_named_t) * ksp->ks_ndata);
 * Now copy the strings to the end of the buffer, and
 * update the pointers appropriately.
         for (i = 0; i < ksp->ks_ndata; i++, knp++)
                 if (knp->data_type == KSTAT_DATA_STRING &&
                     KSTAT_NAMED_STR_PTR(knp) != NULL) {
                         bcopy(KSTAT_NAMED_STR_PTR(knp), end,
                         KSTAT_NAMED_STR_PTR(knp) = end;
                         end += KSTAT_NAMED_STR_BUFLEN(knp);
    return (0);

See Also

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

Writing Device Drivers for Oracle Solaris 11.3