Add a unique "eid" value to all zevents

Tagging each zevent with a unique monotonically increasing EID
(Event IDentifier) provides the required infrastructure for a user
space daemon to reliably process zevents.  By writing the EID to
persistent storage the daemon can safely resume where it left off
in the event stream when it's restarted.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chris Dunlap <cdunlap@llnl.gov>
Issue #2

include/sys/fm/protocol.h

@@ -70,6 +70,7 @@ extern "C" {
 #define	FM_EREPORT_DETECTOR		"detector"
 #define	FM_EREPORT_ENA			"ena"
 #define	FM_EREPORT_TIME			"time"
+#define	FM_EREPORT_EID			"eid"
 
 /* list.* event payload member names */
 #define	FM_LIST_EVENT_SIZE		"list-sz"

include/sys/fm/util.h

@@ -81,6 +81,7 @@ typedef struct zevent_s {
 	list_t		ev_ze_list;	/* " */
 	list_node_t	ev_node;	/* " */
 	zevent_cb_t	*ev_cb;		/* " */
+	uint64_t	ev_eid;
 } zevent_t;
 
 typedef struct zfs_zevent {

module/zfs/fm.c

@@ -84,6 +84,14 @@ static int zevent_len_cur = 0;
 static int zevent_waiters = 0;
 static int zevent_flags = 0;
 
+/*
+ * The EID (Event IDentifier) is used to uniquely tag a zevent when it is
+ * posted.  The posted EIDs are monotonically increasing but not persistent.
+ * They will be reset to the initial value (1) each time the kernel module is
+ * loaded.
+ */
+static uint64_t zevent_eid = 0;
+
 static kmutex_t zevent_lock;
 static list_t zevent_list;
 static kcondvar_t zevent_cv;
@@ -498,6 +506,7 @@ zfs_zevent_post(nvlist_t *nvl, nvlist_t *detector, zevent_cb_t *cb)
 {
 	int64_t tv_array[2];
 	timestruc_t tv;
+	uint64_t eid;
 	size_t nvl_size = 0;
 	zevent_t *ev;
 
@@ -509,6 +518,12 @@ zfs_zevent_post(nvlist_t *nvl, nvlist_t *detector, zevent_cb_t *cb)
 		return;
 	}
 
+	eid = atomic_inc_64_nv(&zevent_eid);
+	if (nvlist_add_uint64(nvl, FM_EREPORT_EID, eid)) {
+		atomic_add_64(&erpt_kstat_data.erpt_set_failed.value.ui64, 1);
+		return;
+	}
+
 	(void) nvlist_size(nvl, &nvl_size, NV_ENCODE_NATIVE);
 	if (nvl_size > ERPT_DATA_SZ || nvl_size == 0) {
 		atomic_add_64(&erpt_kstat_data.erpt_dropped.value.ui64, 1);
@@ -527,6 +542,7 @@ zfs_zevent_post(nvlist_t *nvl, nvlist_t *detector, zevent_cb_t *cb)
 	ev->ev_nvl = nvl;
 	ev->ev_detector = detector;
 	ev->ev_cb = cb;
+	ev->ev_eid = eid;
 
 	mutex_enter(&zevent_lock);
 	zfs_zevent_insert(ev);