Tribblix: manual page: ks

KS_SNAPSHOT(9E) Driver Entry Points KS_SNAPSHOT(9E)

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);
}