Add "zpool nagios" command

(Though it could use improvement, this feature is working.)

The "zpool nagios" command behaves as a Nagios plugin - output a
single line of status information to stdout and exit with a status
code (0=OK, 1=Warning, 2=Critical, 3=Unknown).

There are a few cases that could use improvement for multi-pool
systems, and not all failure scenarios are tested, but it's
certainly a step in the right direction.

TODO:
* Specify pools which must be present on the system
* Additional testing. I don't have a lot of broken pools to mess with.
* Deadman timer of sorts in case ioctls hang

cmd/zpool/Makefile.am

@@ -11,7 +11,8 @@ zpool_SOURCES = \
 	$(top_srcdir)/cmd/zpool/zpool_main.c \
 	$(top_srcdir)/cmd/zpool/zpool_util.c \
 	$(top_srcdir)/cmd/zpool/zpool_util.h \
-	$(top_srcdir)/cmd/zpool/zpool_vdev.c
+	$(top_srcdir)/cmd/zpool/zpool_vdev.c \
+	$(top_srcdir)/cmd/zpool/zpool_nagios.c
 
 zpool_LDADD = \
 	$(top_builddir)/lib/libnvpair/libnvpair.la \

cmd/zpool/zpool_main.c

@@ -59,6 +59,9 @@
 
 #include "statcommon.h"
 
+/* External */
+int zpool_do_nagios(int, char**);
+
 static int zpool_do_create(int, char **);
 static int zpool_do_destroy(int, char **);
 
@@ -139,7 +142,8 @@ typedef enum {
 	HELP_SET,
 	HELP_SPLIT,
 	HELP_REGUID,
-	HELP_REOPEN
+	HELP_REOPEN,
+	HELP_NAGIOS
 } zpool_help_t;
 
 
@@ -193,6 +197,8 @@ static zpool_command_t command_table[] = {
 	{ NULL },
 	{ "get",	zpool_do_get,		HELP_GET		},
 	{ "set",	zpool_do_set,		HELP_SET		},
+	{ NULL },
+	{ "nagios",	zpool_do_nagios,	HELP_NAGIOS		},
 };
 
 #define	NCOMMAND	(sizeof (command_table) / sizeof (command_table[0]))
@@ -276,6 +282,8 @@ get_usage(zpool_help_t idx) {
 		    "[<device> ...]\n"));
 	case HELP_REGUID:
 		return (gettext("\treguid <pool>\n"));
+        case HELP_NAGIOS:
+                return (gettext("\tnagios [-o] [-w] [-c] [pool ...]\n"));
 	}
 
 	abort();