Illumos #1693: persistent 'comment' field for a zpool

Reviewed by: George Wilson <gwilson@zfsmail.com>
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Approved by: Richard Lowe <richlowe@richlowe.net>

References:
  https://www.illumos.org/issues/1693

Ported by: Martin Matuska <martin@matuska.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #678

include/sys/fs/zfs.h

@@ -167,9 +167,13 @@ typedef enum {
 	ZPOOL_PROP_ALLOCATED,
 	ZPOOL_PROP_READONLY,
 	ZPOOL_PROP_ASHIFT,
+	ZPOOL_PROP_COMMENT,
 	ZPOOL_NUM_PROPS
 } zpool_prop_t;
 
+/* Small enough to not hog a whole line of printout in zpool(1M). */
+#define	ZPROP_MAX_COMMENT	32
+
 #define	ZPROP_CONT		-2
 #define	ZPROP_INVAL		-1
 
@@ -500,6 +504,7 @@ typedef struct zpool_rewind_policy {
 #define	ZPOOL_CONFIG_SPLIT_LIST		"guid_list"
 #define	ZPOOL_CONFIG_REMOVING		"removing"
 #define	ZPOOL_CONFIG_RESILVERING	"resilvering"
+#define	ZPOOL_CONFIG_COMMENT		"comment"
 #define	ZPOOL_CONFIG_SUSPENDED		"suspended"	/* not stored on disk */
 #define	ZPOOL_CONFIG_TIMESTAMP		"timestamp"	/* not stored on disk */
 #define	ZPOOL_CONFIG_BOOTFS		"bootfs"	/* not stored on disk */

include/sys/spa_impl.h

@@ -112,6 +112,7 @@ struct spa {
 	 * Fields protected by spa_namespace_lock.
 	 */
 	char		spa_name[MAXNAMELEN];	/* pool name */
+	char		*spa_comment;		/* comment */
 	avl_node_t	spa_avl;		/* node in spa_namespace_avl */
 	nvlist_t	*spa_config;		/* last synced config */
 	nvlist_t	*spa_config_syncing;	/* currently syncing config */

include/sys/zfs_context.h

@@ -60,6 +60,7 @@
 #include <sys/zfs_debug.h>
 #include <sys/fm/fs/zfs.h>
 #include <sys/sunddi.h>
+#include <sys/ctype.h>
 #include <linux/dcache_compat.h>
 
 #else /* _KERNEL */
@@ -92,6 +93,7 @@
 #include <atomic.h>
 #include <dirent.h>
 #include <time.h>
+#include <ctype.h>
 #include <sys/note.h>
 #include <sys/types.h>
 #include <sys/cred.h>