Add -y option to `zpool iostat`

sysstat's iostat omits the first report when the -y option is used.
This patch adds that functionality and omits the first report with
statistics since system boot.

Signed-off-by: Hajo Möller <dasjoe@gmail.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3439

cmd/zpool/zpool_main.c

@@ -236,8 +236,8 @@ get_usage(zpool_help_t idx) {
 		    "[-R root] [-F [-n]]\n"
 		    "\t    <pool | id> [newpool]\n"));
 	case HELP_IOSTAT:
-		return (gettext("\tiostat [-v] [-T d|u] [pool] ... [interval "
+		return (gettext("\tiostat [-v] [-T d|u] [-y] [pool] ... "
-		    "[count]]\n"));
+		    "[interval [count]]\n"));
 	case HELP_LABELCLEAR:
 		return (gettext("\tlabelclear [-f] <vdev>\n"));
 	case HELP_LIST:
@@ -2817,10 +2817,11 @@ zpool_do_iostat(int argc, char **argv)
 	unsigned long interval = 0, count = 0;
 	zpool_list_t *list;
 	boolean_t verbose = B_FALSE;
+	boolean_t omit_since_boot = B_FALSE;
 	iostat_cbdata_t cb;
 
 	/* check options */
-	while ((c = getopt(argc, argv, "T:v")) != -1) {
+	while ((c = getopt(argc, argv, "T:vy")) != -1) {
 		switch (c) {
 		case 'T':
 			get_timestamp_arg(*optarg);
@@ -2828,6 +2829,9 @@ zpool_do_iostat(int argc, char **argv)
 		case 'v':
 			verbose = B_TRUE;
 			break;
+		case 'y':
+			omit_since_boot = B_TRUE;
+			break;
 		case '?':
 			(void) fprintf(stderr, gettext("invalid option '%c'\n"),
 			    optopt);
@@ -2867,11 +2871,16 @@ zpool_do_iostat(int argc, char **argv)
 	cb.cb_namewidth = 0;
 
 	for (;;) {
-		pool_list_update(list);
-
 		if ((npools = pool_list_count(list)) == 0)
 			(void) fprintf(stderr, gettext("no pools available\n"));
 		else {
+			/*
+			 * If this is the first iteration and -y was supplied
+			 * we skip any printing.
+			 */
+			boolean_t skip = (omit_since_boot &&
+				cb.cb_iteration == 0);
+
 			/*
 			 * Refresh all statistics.  This is done as an
 			 * explicit step before calculating the maximum name
@@ -2893,12 +2902,18 @@ zpool_do_iostat(int argc, char **argv)
 				print_timestamp(timestamp_fmt);
 
 			/*
-			 * If it's the first time, or verbose mode, print the
+			 * If it's the first time and we're not skipping it,
-			 * header.
+			 * or either skip or verbose mode, print the header.
 			 */
-			if (++cb.cb_iteration == 1 || verbose)
+			if ((++cb.cb_iteration == 1 && !skip) ||
+				(skip != verbose))
 				print_iostat_header(&cb);
 
+			if (skip) {
+				(void) sleep(interval);
+				continue;
+			}
+
 			(void) pool_list_iter(list, B_FALSE, print_iostat, &cb);
 
 			/*

man/man8/zpool.8

@@ -94,7 +94,7 @@ zpool \- configures ZFS storage pools
 
 .LP
 .nf
-\fBzpool iostat\fR [\fB-T\fR d | u ] [\fB-v\fR] [\fIpool\fR] ... [\fIinterval\fR[\fIcount\fR]]
+\fBzpool iostat\fR [\fB-T\fR d | u ] [\fB-v\fR] [\fB-y\fR] [\fIpool\fR] ... [\fIinterval\fR[\fIcount\fR]]
 .fi
 
 .LP
@@ -1608,7 +1608,7 @@ Allows a pool to import when there is a missing log device.
 .ne 2
 .mk
 .na
-\fB\fBzpool iostat\fR [\fB-T\fR \fBd\fR | \fBu\fR] [\fB-v\fR] [\fIpool\fR] ... [\fIinterval\fR[\fIcount\fR]]\fR
+\fB\fBzpool iostat\fR [\fB-T\fR \fBd\fR | \fBu\fR] [\fB-v\fR] [\fB-y\fR] [\fIpool\fR] ... [\fIinterval\fR[\fIcount\fR]]\fR
 .ad
 .sp .6
 .RS 4n
@@ -1637,6 +1637,17 @@ Specify \fBu\fR for a printed representation of the internal representation of t
 Verbose statistics. Reports usage statistics for individual \fIvdevs\fR within the pool, in addition to the pool-wide statistics.
 .RE
 
+.sp
+.ne 2
+.mk
+.na
+\fB\fB-y\fR\fR
+.ad
+.RS 12n
+.rt
+Omit statistics since boot.  Normally the first line of output reports the statistics since boot.  This option suppresses that first line of output.
+.RE
+
 .RE
 
 .sp