'\" te
.\" Copyright (c) 1994, Sun Microsystems, Inc., All Rights Reserved
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.  See the License for the specific language governing permissions and limitations under the License.
.\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE.  If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner]
.TH KS_UPDATE 9E "May 27, 1994"
.SH NAME
ks_update \- dynamically update kstats
.SH SYNOPSIS
.nf
#include <sys/types.h>
#include <sys/kstat.h>
#include <sys/ddi.h>
#include <sys/sunddi.h>



\fBint prefix\fR\fB_ks_update\fR(\fBkstat_t *\fR\fIksp\fR, \fBint\fR \fIrw\fR);
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI)
.SH PARAMETERS
.ne 2
.na
\fB\fIksp\fR \fR
.ad
.RS 8n
Pointer to a \fBkstat\fR(9S) structure.
.RE

.sp
.ne 2
.na
\fB\fIrw\fR \fR
.ad
.RS 8n
Read/Write flag. Possible values are
.sp
.ne 2
.na
\fB\fBKSTAT_READ\fR \fR
.ad
.RS 16n
Update \fBkstat\fR structure statistics from the driver.
.RE

.sp
.ne 2
.na
\fB\fBKSTAT_WRITE\fR \fR
.ad
.RS 16n
Update driver statistics from the kstat structure.
.RE

.RE

.SH DESCRIPTION
The kstat mechanism allows for an optional \fBks_update()\fR 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
\fBks_update()\fR function which updates the kstat's data section on demand. To
take advantage of this feature, set the  \fBks_update\fR field before calling
\fBkstat_install\fR(9F).
.sp
.LP
The \fBks_update()\fR function must have the following structure:
.sp
.in +2
.nf
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);
}
.fi
.in -2

.sp
.LP
In general, the \fBks_update()\fR routine may need to refer to provider-private
data; for example, it may need a pointer to the provider's raw statistics.  The
\fBks_private\fR field is available for this purpose.   Its use is entirely at
the provider's discretion.
.sp
.LP
No \fBkstat\fR locking should be done inside the \fBks_update()\fR routine.
The caller will already be holding the \fBkstat's\fR  \fBks_lock\fR (to ensure
consistent data) and will prevent the \fBkstat\fR from being removed.
.SH RETURN VALUES
\fBks_update()\fR should return
.sp
.ne 2
.na
\fB\fB0\fR \fR
.ad
.RS 11n
For success.
.RE

.sp
.ne 2
.na
\fB\fBEACCES\fR \fR
.ad
.RS 11n
If \fBKSTAT_WRITE\fR is not allowed.
.RE

.sp
.ne 2
.na
\fB\fBEIO\fR \fR
.ad
.RS 11n
For any other error.
.RE

.SH SEE ALSO
\fBkstat_create\fR(9F), \fBkstat_install\fR(9F), \fBkstat\fR(9S)
.sp
.LP
\fIWriting Device Drivers\fR