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 KS_SNAPSHOT 9E "Sep 7, 2015"
 NAME
ks_snapshot - take a snapshot of kstat data

 SYNOPSIS
#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
illumos DDI specific (illumos DDI).

 PARAMETERS
ksp 


Pointer to a kstat(9S) structure.



buf 


Pointer to a buffer to copy the snapshot into.



rw 


Read/Write flag. Possible values are:
KSTAT_READ


Copy driver statistics from the driver to the buffer.



KSTAT_WRITE


Copy statistics from the buffer to the driver.







 DESCRIPTION
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_snapshot() 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
0


Success



EACCES


If KSTAT_WRITE is not allowed



EIO


For any other error




 CONTEXT
This function is called from user context only.

 EXAMPLES
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_BUFLEN(knp));
 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