lvmetad: preemptively check and rescan in commands

Move checking the lvmetad state, and the possible rescan,
out of lvmetad_send() to the start of the command.

Previously, the token mismatch and rescan would occur
within lvmetad_send() for some other request.  Now,
the token mismatch is detected earlier, so the
rescan can be done before the main command is in
progress.  Rescanning deep within the processing of
another command will disturb the lvmcache state of
that other command.

A rescan already exists at the start of the command
for the case where foreign VGs are going to be read.
This same rescan is now also performed when there is
an lvmetad token mismatch (from a changed global_filter).

The commands pvscan/vgscan/lvscan/vgimport are excluded
from this preemptive checking/rescanning for lvmetad
because they want to do rescanning themselves explicitly.

If rescanning devices fails, then lvmetad has not been
correctly repopulated and should not be used, so make
the command revert to not using lvmetad.

11 files changed, 417 insertions, 110 deletions

diff --git a/lib/cache/lvmetad.c b/lib/cache/lvmetad.c
index a483e04e3..0f353cc61 100644
--- a/lib/cache/lvmetad.c
+++ b/lib/cache/lvmetad.c
@@ -24,6 +24,8 @@
 #include "lvm-signal.h"
 #include "lvmlockd.h"
 
+#include <time.h>
+
 #define SCAN_TIMEOUT_SECONDS	80
 #define MAX_RESCANS		10	/* Maximum number of times to scan all PVs and retry if the daemon returns a token mismatch error */
 
@@ -210,67 +212,227 @@ void lvmetad_set_socket(const char *sock)
 	_lvmetad_socket = sock;
 }
 
+/*
+ * Check if lvmetad's token matches our token.  The token is a hash
+ * of the global filter used to populate lvmetad.  The lvmetad token
+ * was set by the last command to populate lvmetad, and it was set to
+ * the hash of the global filter that command used when scanning to
+ * populate lvmetad.
+ *
+ * Our token is a hash of the global filter this command is using.
+ *
+ * If the lvmetad token is not set (or "none"), then lvmetad has not
+ * been populated.  If the lvmetad token is "update in progress", then
+ * lvmetad is currently being populated (this should be temporary).
+ * If the lvmetad token otherwise differs from ours, then lvmetad was
+ * populated using a different global filter that we are using.
+ *
+ * Return 1 if the lvmetad token matches ours.  We can use it as is.
+ *
+ * Return 0 if the lvmetad token does not match ours (lvmetad is
+ * empty or populated using a different global filter).
+ * We cannot use the lvmetad cache until we repopulate it
+ * (and set lvmetad's token to match ours.)
+ *
+ * If there's some other error, disable this command's use of
+ * lvmetad, so it will revert to disk scanning.  In this
+ * case return 0.
+ */
+
+int lvmetad_token_matches(struct cmd_context *cmd)
+{
+	daemon_reply reply;
+	const char *daemon_token;
+	unsigned int delay_usec = 0;
+	unsigned int wait_sec = 0;
+	uint64_t now = 0, wait_start = 0;
+	int ret = 1;
+
+	wait_sec = (unsigned int)find_config_tree_int(cmd, global_lvmetad_update_wait_time_CFG, NULL);
+
+retry:
+	log_debug_lvmetad("lvmetad send get_global_info");
+
+	reply = daemon_send_simple(_lvmetad, "get_global_info",
+				   "token = %s", "skip",
+				   NULL);
+	if (reply.error) {
+		log_warn("WARNING: Not using lvmetad after send error (%d).", reply.error);
+		goto fail;
+	}
+
+	if (strcmp(daemon_reply_str(reply, "response", ""), "OK")) {
+		log_warn("WARNING: Not using lvmetad after response error.");
+		goto fail;
+	}
+
+	if (!(daemon_token = daemon_reply_str(reply, "token", NULL))) {
+		log_warn("WARNING: Not using lvmetad after missing token.");
+		goto fail;
+	}
+
+	/*
+	 * If lvmetad is being updated by another command, then sleep and retry
+	 * until the token shows the update is done, and go on to the token
+	 * comparison.
+	 *
+	 * Between retries, sleep for a random period between 1 and 2 seconds.
+	 * Retry in this way for up to a configurable period of time.
+	 *
+	 * If lvmetad is still being updated after the timeout period,
+	 * then disable this command's use of lvmetad.
+	 *
+	 * (lvmetad could return the number of objects in its cache along with
+	 * the update message so that callers could detect when a rescan has
+	 * stalled while updating lvmetad.)
+	 */
+	if (!strcmp(daemon_token, "update in progress")) {
+		now = (uint64_t)time(NULL);
+
+		if (!wait_start)
+			wait_start = now;
+
+		if (now - wait_start >= wait_sec) {
+			log_warn("WARNING: Not using lvmetad after %u sec lvmetad_update_wait_time.", wait_sec);
+			goto fail;
+		}
+
+		log_warn("WARNING: lvmetad is being updated, retrying (setup) for %u more seconds.",
+			 wait_sec - (unsigned int)(now - wait_start));
+
+		/* Delay a random period between 1 and 2 seconds. */
+		delay_usec = 1000000 + lvm_even_rand(&_lvmetad_cmd->rand_seed, 1000000);
+		usleep(delay_usec);
+		daemon_reply_destroy(reply);
+		goto retry;
+	}
+
+	/*
+	 * lvmetad is empty, not yet populated.
+	 * The caller should do a disk scan to populate lvmetad.
+	 */
+	if (!strcmp(daemon_token, "none")) {
+		ret = 0;
+		goto out;
+	}
+
+	/*
+	 * lvmetad has an unmatching token; it was last populated using
+	 * a different global filter.
+	 * The caller should do a disk scan to populate lvmetad with
+	 * our global filter.
+	 */
+	if (strcmp(daemon_token, _lvmetad_token)) {
+		ret = 0;
+		goto out;
+	}
+
+out:
+	daemon_reply_destroy(reply);
+	return ret;
+
+fail:
+	daemon_reply_destroy(reply);
+	/* The command will not use lvmetad and will revert to scanning. */
+	lvmetad_set_active(cmd, 0);
+	return 0;
+}
+
 static int _lvmetad_pvscan_all_devs(struct cmd_context *cmd, activation_handler handler,
 				    int ignore_obsolete);
 
-static daemon_reply _lvmetad_send(const char *id, ...)
+static daemon_reply _lvmetad_send(struct cmd_context *cmd, const char *id, ...)
 {
 	va_list ap;
-	daemon_reply repl = { 0 };
+	daemon_reply reply = { 0 };
 	daemon_request req;
-	unsigned num_rescans = 0;
-	unsigned total_usecs_waited = 0;
-	unsigned max_remaining_sleep_times = 1;
-	unsigned wait_usecs;
+	unsigned int delay_usec;
+	unsigned int wait_sec = 0;
+	uint64_t now = 0, wait_start = 0;
 
+	if (cmd)
+		wait_sec = (unsigned int)find_config_tree_int(cmd, global_lvmetad_update_wait_time_CFG, NULL);
 retry:
+	log_debug_lvmetad("lvmetad_send %s", id);
+
 	req = daemon_request_make(id);
 
 	if (_lvmetad_token && !daemon_request_extend(req, "token = %s", _lvmetad_token, NULL)) {
-		repl.error = ENOMEM;
-		return repl;
+		reply.error = ENOMEM;
+		return reply;
 	}
 
 	va_start(ap, id);
 	daemon_request_extend_v(req, ap);
 	va_end(ap);
 
-	repl = daemon_send(_lvmetad, req);
+	reply = daemon_send(_lvmetad, req);
 
 	daemon_request_destroy(req);
 
-	/*
-	 * If another process is trying to scan, it might have the
-	 * same future token id and it's better to wait and avoid doing
-	 * the work multiple times. For the case where the future token is
-	 * different, the wait is randomized so that multiple waiting
-	 * processes do not start scanning all at once.
-	 *
-	 * If the token is mismatched because of global_filter changes,
-	 * we re-scan immediately, but if we lose the potential race for
-	 * the update, we back off for a short while (0.05-0.5 seconds) and
-	 * try again.
-	 */
-	if (!repl.error && !strcmp(daemon_reply_str(repl, "response", ""), "token_mismatch") &&
-	    num_rescans < MAX_RESCANS && total_usecs_waited < (SCAN_TIMEOUT_SECONDS * 1000000) && !test_mode()) {
-		if (!strcmp(daemon_reply_str(repl, "expected", ""), "update in progress") ||
-		    max_remaining_sleep_times) {
-			wait_usecs = 50000 + lvm_even_rand(&_lvmetad_cmd->rand_seed, 450000); /* between 0.05s and 0.5s */
-			(void) usleep(wait_usecs);
-			total_usecs_waited += wait_usecs;
-			if (max_remaining_sleep_times)
-				max_remaining_sleep_times--;	/* Sleep once before rescanning the first time, then 5 times each time after that. */
+	if (reply.error)
+		goto out;
+
+	if (!strcmp(daemon_reply_str(reply, "response", ""), "token_mismatch")) {
+		if (!strcmp(daemon_reply_str(reply, "expected", ""), "update in progress")) {
+			/*
+			 * Another command is updating the lvmetad cache, and
+			 * we cannot use lvmetad until the update is finished.
+			 * Retry our request for a while; the update should
+			 * finish shortly.  This should not usually happen
+			 * because this command already checked that the token
+			 * is usable in lvmetad_token_matches(), but it's
+			 * possible for another command's rescan to slip in
+			 * between the time we call lvmetad_token_matches()
+			 * and the time we get here to lvmetad_send().
+			 */
+			now = time(NULL);
+
+			if (!wait_start)
+				wait_start = now;
+
+			if (!wait_sec || (now - wait_start >= wait_sec)) {
+				log_warn("WARNING: Cannot use lvmetad after %u sec lvmetad_update_wait_time.", wait_sec);
+				goto out;
+			}
+
+			log_warn("WARNING: lvmetad is being updated, retrying (%s) for %u more seconds.",
+				 id, wait_sec - (unsigned int)(now - wait_start));
+
+			/* Delay a random period between 1 and 2 seconds. */
+			delay_usec = 1000000 + lvm_even_rand(&_lvmetad_cmd->rand_seed, 1000000);
+			usleep(delay_usec);
+			daemon_reply_destroy(reply);
+			goto retry;
 		} else {
-			/* If the re-scan fails here, we try again later. */
-			(void) _lvmetad_pvscan_all_devs(_lvmetad_cmd, NULL, 0);
-			num_rescans++;
-			max_remaining_sleep_times = 5;
+			/*
+			 * Another command has updated the lvmetad cache, and
+			 * has done so using a different device filter from our
+			 * own, which has made the lvmetad token and our token
+			 * not match.  This should not usually happen because
+			 * this command has already checked for a matching token
+			 * in lvmetad_token_matches(), but it's possible for
+			 * another command's rescan to slip in between the time
+			 * we call lvmetad_token_matches() and the time we get
+			 * here to lvmetad_send().  With a mismatched token
+			 * (different set of devices), we cannot use the lvmetad
+			 * cache.
+			 *
+			 * FIXME: it would be nice to have this command ignore
+			 * lvmetad at this point and revert to disk scanning,
+			 * but the layers above lvmetad_send are not yet able
+			 * to switch modes in the middle of processing.
+			 *
+			 * (The advantage of lvmetad_check_token is that it
+			 * can rescan to get the token in sync, or if that
+			 * fails it can make the command revert to scanning
+			 * from the start.)
+			 */
+			log_warn("WARNING: Cannot use lvmetad while it caches different devices.");
 		}
-		daemon_reply_destroy(repl);
-		goto retry;
 	}
-
-	return repl;
+out:
+	return reply;
 }
 
 static int _token_update(void)
@@ -278,7 +440,7 @@ static int _token_update(void)
 	daemon_reply repl;
 
 	log_debug_lvmetad("Sending updated token to lvmetad: %s", _lvmetad_token ? : "<NONE>");
-	repl = _lvmetad_send("token_update", NULL);
+	repl = _lvmetad_send(NULL, "token_update", NULL);
 
 	if (repl.error || strcmp(daemon_reply_str(repl, "response", ""), "OK")) {
 		daemon_reply_destroy(repl);
@@ -297,13 +459,68 @@ static int _token_update(void)
  * If found is set, *found indicates whether or not device exists,
  * and missing device is not treated as an error.
  */
-static int _lvmetad_handle_reply(daemon_reply reply, const char *action, const char *object,
-				 int *found)
+static int _lvmetad_handle_reply(daemon_reply reply, const char *id, const char *object, int *found)
 {
+	int action_modifies = 0;
+	const char *action;
+
+	if (!id)
+		action = "<none>";
+	else if (!strcmp(id, "pv_list"))
+		action = "list PVs";
+	else if (!strcmp(id, "vg_list"))
+		action = "list VGs";
+	else if (!strcmp(id, "vg_lookup"))
+		action = "lookup VG";
+	else if (!strcmp(id, "pv_lookup"))
+		action = "lookup PV";
+	else if (!strcmp(id, "pv_clear_all"))
+		action = "clear info about all PVs";
+	else if (!strcmp(id, "vg_clear_outdated_pvs"))
+		action = "clear the list of outdated PVs";
+	else if (!strcmp(id, "vg_update")) {
+		action = "update VG";
+		action_modifies = 1;
+	} else if (!strcmp(id, "vg_remove")) {
+		action = "remove VG";
+		action_modifies = 1;
+	} else if (!strcmp(id, "pv_found")) {
+		action = "update PV";
+		action_modifies = 1;
+	} else if (!strcmp(id, "pv_gone")) {
+		action = "drop PV";
+		action_modifies = 1;
+	} else {
+		log_error(INTERNAL_ERROR "Unchecked lvmetad message %s.", id);
+		action = "action unknown";
+	}
+
 	if (reply.error) {
 		log_error("Request to %s %s%sin lvmetad gave response %s.",
 			  action, object, *object ? " " : "", strerror(reply.error));
-		return 0;
+		goto fail;
+	}
+
+	/*
+	 * See the description of the token mismatch errors in lvmetad_send.
+	 */
+	if (!strcmp(daemon_reply_str(reply, "response", ""), "token_mismatch")) {
+		if (!strcmp(daemon_reply_str(reply, "expected", ""), "update in progress")) {
+			/*
+			 * lvmetad_send retried up to the limit and eventually
+			 * printed a warning and gave up.
+			 */
+			log_error("Request to %s %s%sin lvmetad failed after lvmetad_update_wait_time expired.",
+				  action, object, *object ? " " : "");
+		} else {
+			/*
+			 * lvmetad is caching different devices based on a different
+			 * device filter which causes a token mismatch.
+			 */
+			log_error("Request to %s %s%sin lvmetad failed after device filter mismatch.",
+				  action, object, *object ? " " : "");
+		}
+		goto fail;
 	}
 
 	/* All OK? */
@@ -330,10 +547,23 @@ static int _lvmetad_handle_reply(daemon_reply reply, const char *action, const c
 		return 1;
 	}
 
+	/*
+	 * Generic error message for error cases not specifically checked above.
+	 */
 	log_error("Request to %s %s%sin lvmetad gave response %s. Reason: %s",
 		  action, object, *object ? " " : "", 
 		  daemon_reply_str(reply, "response", "<missing>"),
 		  daemon_reply_str(reply, "reason", "<missing>"));
+fail:
+	/*
+	 * If the failed lvmetad message was updating lvmetad, it is important
+	 * to restart lvmetad (or at least rescan.)
+	 *
+	 * FIXME: attempt to set the disabled state in lvmetad here so that
+	 * commands will not use it until it's been properly repopulated.
+	 */
+	if (action_modifies)
+		log_error("lvmetad update failed.  Restart lvmetad immediately.");
 
 	return 0;
 }
@@ -537,7 +767,7 @@ struct volume_group *lvmetad_vg_lookup(struct cmd_context *cmd, const char *vgna
 
 	if (vgid && vgname) {
 		log_debug_lvmetad("Asking lvmetad for VG %s %s", uuid, vgname);
-		reply = _lvmetad_send("vg_lookup",
+		reply = _lvmetad_send(cmd, "vg_lookup",
 				      "uuid = %s", uuid,
 				      "name = %s", vgname,
 				      NULL);
@@ -545,12 +775,12 @@ struct volume_group *lvmetad_vg_lookup(struct cmd_context *cmd, const char *vgna
 
 	} else if (vgid) {
 		log_debug_lvmetad("Asking lvmetad for VG vgid %s", uuid);
-		reply = _lvmetad_send("vg_lookup", "uuid = %s", uuid, NULL);
+		reply = _lvmetad_send(cmd, "vg_lookup", "uuid = %s", uuid, NULL);
 		diag_name = uuid;
 
 	} else if (vgname) {
 		log_debug_lvmetad("Asking lvmetad for VG %s", vgname);
-		reply = _lvmetad_send("vg_lookup", "name = %s", vgname, NULL);
+		reply = _lvmetad_send(cmd, "vg_lookup", "name = %s", vgname, NULL);
 		diag_name = vgname;
 
 	} else {
@@ -558,7 +788,7 @@ struct volume_group *lvmetad_vg_lookup(struct cmd_context *cmd, const char *vgna
 		goto out;
 	}
 
-	if (_lvmetad_handle_reply(reply, "lookup VG", diag_name, &found) && found) {
+	if (_lvmetad_handle_reply(reply, "vg_lookup", diag_name, &found) && found) {
 
 		if ((found == 2) && vgname) {
 			log_error("Multiple VGs found with the same name: %s.", vgname);
@@ -718,10 +948,10 @@ int lvmetad_vg_update(struct volume_group *vg)
 	}
 
 	log_debug_lvmetad("Sending lvmetad updated metadata for VG %s (seqno %" PRIu32 ")", vg->name, vg->seqno);
-	reply = _lvmetad_send("vg_update", "vgname = %s", vg->name,
+	reply = _lvmetad_send(vg->cmd, "vg_update", "vgname = %s", vg->name,
 			      "metadata = %t", vg->cft_precommitted, NULL);
 
-	if (!_lvmetad_handle_reply(reply, "update VG", vg->name, NULL)) {
+	if (!_lvmetad_handle_reply(reply, "vg_update", vg->name, NULL)) {
 		daemon_reply_destroy(reply);
 		return 0;
 	}
@@ -770,8 +1000,8 @@ int lvmetad_vg_remove(struct volume_group *vg)
 		return_0;
 
 	log_debug_lvmetad("Telling lvmetad to remove VGID %s (%s)", uuid, vg->name);
-	reply = _lvmetad_send("vg_remove", "uuid = %s", uuid, NULL);
-	result = _lvmetad_handle_reply(reply, "remove VG", vg->name, NULL);
+	reply = _lvmetad_send(vg->cmd, "vg_remove", "uuid = %s", uuid, NULL);
+	result = _lvmetad_handle_reply(reply, "vg_remove", vg->name, NULL);
 
 	daemon_reply_destroy(reply);
 
@@ -792,8 +1022,8 @@ int lvmetad_pv_lookup(struct cmd_context *cmd, struct id pvid, int *found)
 		return_0;
 
 	log_debug_lvmetad("Asking lvmetad for PV %s", uuid);
-	reply = _lvmetad_send("pv_lookup", "uuid = %s", uuid, NULL);
-	if (!_lvmetad_handle_reply(reply, "lookup PV", "", found))
+	reply = _lvmetad_send(cmd, "pv_lookup", "uuid = %s", uuid, NULL);
+	if (!_lvmetad_handle_reply(reply, "pv_lookup", "", found))
 		goto_out;
 
 	if (found && !*found)
@@ -823,8 +1053,8 @@ int lvmetad_pv_lookup_by_dev(struct cmd_context *cmd, struct device *dev, int *f
 		return_0;
 
 	log_debug_lvmetad("Asking lvmetad for PV on %s", dev_name(dev));
-	reply = _lvmetad_send("pv_lookup", "device = %" PRId64, (int64_t) dev->dev, NULL);
-	if (!_lvmetad_handle_reply(reply, "lookup PV", dev_name(dev), found))
+	reply = _lvmetad_send(cmd, "pv_lookup", "device = %" PRId64, (int64_t) dev->dev, NULL);
+	if (!_lvmetad_handle_reply(reply, "pv_lookup", dev_name(dev), found))
 		goto_out;
 
 	if (found && !*found)
@@ -852,8 +1082,8 @@ int lvmetad_pv_list_to_lvmcache(struct cmd_context *cmd)
 		return 1;
 
 	log_debug_lvmetad("Asking lvmetad for complete list of known PVs");
-	reply = _lvmetad_send("pv_list", NULL);
-	if (!_lvmetad_handle_reply(reply, "list PVs", "", NULL)) {
+	reply = _lvmetad_send(cmd, "pv_list", NULL);
+	if (!_lvmetad_handle_reply(reply, "pv_list", "", NULL)) {
 		daemon_reply_destroy(reply);
 		return_0;
 	}
@@ -877,8 +1107,8 @@ int lvmetad_get_vgnameids(struct cmd_context *cmd, struct dm_list *vgnameids)
 	struct dm_config_node *cn;
 
 	log_debug_lvmetad("Asking lvmetad for complete list of known VG ids/names");
-	reply = _lvmetad_send("vg_list", NULL);
-	if (!_lvmetad_handle_reply(reply, "list VGs", "", NULL)) {
+	reply = _lvmetad_send(cmd, "vg_list", NULL);
+	if (!_lvmetad_handle_reply(reply, "vg_list", "", NULL)) {
 		daemon_reply_destroy(reply);
 		return_0;
 	}
@@ -930,8 +1160,8 @@ int lvmetad_vg_list_to_lvmcache(struct cmd_context *cmd)
 		return 1;
 
 	log_debug_lvmetad("Asking lvmetad for complete list of known VGs");
-	reply = _lvmetad_send("vg_list", NULL);
-	if (!_lvmetad_handle_reply(reply, "list VGs", "", NULL)) {
+	reply = _lvmetad_send(cmd, "vg_list", NULL);
+	if (!_lvmetad_handle_reply(reply, "vg_list", "", NULL)) {
 		daemon_reply_destroy(reply);
 		return_0;
 	}
@@ -1089,7 +1319,7 @@ int lvmetad_pv_found(const struct id *pvid, struct device *dev, const struct for
 		}
 
 		log_debug_lvmetad("Telling lvmetad to store PV %s (%s) in VG %s", dev_name(dev), uuid, vg->name);
-		reply = _lvmetad_send("pv_found",
+		reply = _lvmetad_send(vg->cmd, "pv_found",
 				      "pvmeta = %t", pvmeta,
 				      "vgname = %s", vg->name,
 				      "metadata = %t", vgmeta,
@@ -1101,12 +1331,12 @@ int lvmetad_pv_found(const struct id *pvid, struct device *dev, const struct for
 		 * It might or might not be an orphan.
 		 */
 		log_debug_lvmetad("Telling lvmetad to store PV %s (%s)", dev_name(dev), uuid);
-		reply = _lvmetad_send("pv_found", "pvmeta = %t", pvmeta, NULL);
+		reply = _lvmetad_send(NULL, "pv_found", "pvmeta = %t", pvmeta, NULL);
 	}
 
 	dm_config_destroy(pvmeta);
 
-	result = _lvmetad_handle_reply(reply, "update PV", uuid, NULL);
+	result = _lvmetad_handle_reply(reply, "pv_found", uuid, NULL);
 
 	if (vg && result &&
 	    (daemon_reply_int(reply, "seqno_after", -1) != vg->seqno ||
@@ -1196,9 +1426,9 @@ int lvmetad_pv_gone(dev_t devno, const char *pv_name, activation_handler handler
 	 */
 
 	log_debug_lvmetad("Telling lvmetad to forget any PV on %s", pv_name);
-	reply = _lvmetad_send("pv_gone", "device = %" PRId64, (int64_t) devno, NULL);
+	reply = _lvmetad_send(NULL, "pv_gone", "device = %" PRId64, (int64_t) devno, NULL);
 
-	result = _lvmetad_handle_reply(reply, "drop PV", pv_name, &found);
+	result = _lvmetad_handle_reply(reply, "pv_gone", pv_name, &found);
 	/* We don't care whether or not the daemon had the PV cached. */
 
 	daemon_reply_destroy(reply);
@@ -1431,10 +1661,6 @@ int lvmetad_pvscan_single(struct cmd_context *cmd, struct device *dev,
 	return 1;
 
 bad:
-	/* FIXME kill lvmetad automatically if we can */
-	log_error("Update of lvmetad failed. This is a serious problem.\n"
-		  "It is strongly recommended that you restart lvmetad immediately.");
-
 	return 0;
 }
 
@@ -1453,6 +1679,8 @@ static int _lvmetad_pvscan_all_devs(struct cmd_context *cmd, activation_handler
 		return 0;
 	}
 
+	log_debug_lvmetad("Scanning all devices to update lvmetad.");
+
 	if (!(iter = dev_iter_create(cmd->lvmetad_filter, 1))) {
 		log_error("dev_iter creation failed");
 		return 0;
@@ -1467,8 +1695,8 @@ static int _lvmetad_pvscan_all_devs(struct cmd_context *cmd, activation_handler
 	}
 
 	log_debug_lvmetad("Telling lvmetad to clear its cache");
-	reply = _lvmetad_send("pv_clear_all", NULL);
-	if (!_lvmetad_handle_reply(reply, "clear info about all PVs", "", NULL))
+	reply = _lvmetad_send(cmd, "pv_clear_all", NULL);
+	if (!_lvmetad_handle_reply(reply, "pv_clear_all", "", NULL))
 		r = 0;
 	daemon_reply_destroy(reply);
 
@@ -1519,8 +1747,8 @@ int lvmetad_vg_clear_outdated_pvs(struct volume_group *vg)
 	if (!id_write_format(&vg->id, uuid, sizeof(uuid)))
 		return_0;
 
-	reply = _lvmetad_send("vg_clear_outdated_pvs", "vgid = %s", uuid, NULL);
-	result = _lvmetad_handle_reply(reply, "clear the list of outdated PVs", vg->name, NULL);
+	reply = _lvmetad_send(vg->cmd, "vg_clear_outdated_pvs", "vgid = %s", uuid, NULL);
+	result = _lvmetad_handle_reply(reply, "vg_clear_outdated_pvs", vg->name, NULL);
 	daemon_reply_destroy(reply);
 
 	return result;
@@ -1555,9 +1783,8 @@ static int _lvmetad_get_pv_cache_list(struct cmd_context *cmd, struct dm_list *p
 
 	log_debug_lvmetad("Asking lvmetad for complete list of known PVs");
 
-	reply = _lvmetad_send("pv_list", NULL);
-	if (!_lvmetad_handle_reply(reply, "list PVs", "", NULL)) {
-		log_error("lvmetad message failed.");
+	reply = _lvmetad_send(cmd, "pv_list", NULL);
+	if (!_lvmetad_handle_reply(reply, "pv_list", "", NULL)) {
 		daemon_reply_destroy(reply);
 		return_0;
 	}
@@ -1752,6 +1979,8 @@ void lvmetad_validate_global_cache(struct cmd_context *cmd, int force)
 	if (force)
 		goto do_scan;
 
+	log_debug_lvmetad("lvmetad validate send get_global_info");
+
 	reply = daemon_send_simple(_lvmetad, "get_global_info",
 				   "token = %s", "skip",
 				   NULL);
@@ -1782,10 +2011,18 @@ void lvmetad_validate_global_cache(struct cmd_context *cmd, int force)
 
 	/*
 	 * Update the local lvmetad cache so it correctly reflects any
-	 * changes made on remote hosts.
+	 * changes made on remote hosts.  (It's possible that this command
+	 * already refreshed the local lvmetad because of a token change,
+	 * but we need to do it again here since we now hold the global
+	 * lock.  Another host may have changed things between the time
+	 * we rescanned for the token, and the time we acquired the global
+	 * lock.)
 	 */
-	if (!lvmetad_pvscan_all_devs(cmd, NULL))
-		stack; /* FIXME: Anything more on this error path ? */
+	if (!lvmetad_pvscan_all_devs(cmd, NULL)) {
+		log_warn("WARNING: Not using lvmetad because device scan failed.");
+		lvmetad_set_active(cmd, 0);
+		return;
+	}
 
 	/*
 	 * Clear the global_invalid flag in lvmetad.
@@ -1793,6 +2030,8 @@ void lvmetad_validate_global_cache(struct cmd_context *cmd, int force)
 	 * from lvmetad will not see global_invalid until
 	 * another host makes another global change.
 	 */
+	log_debug_lvmetad("lvmetad validate send set_global_info");
+
 	reply = daemon_send_simple(_lvmetad, "set_global_info",
 				   "token = %s", "skip",
 				   "global_invalid = " FMTd64, INT64_C(0),
@@ -1842,7 +2081,7 @@ int lvmetad_vg_is_foreign(struct cmd_context *cmd, const char *vgname, const cha
 	if (!id_write_format((const struct id*)vgid, uuid, sizeof(uuid)))
 		return_0;
 
-	reply = _lvmetad_send("vg_lookup",
+	reply = _lvmetad_send(cmd, "vg_lookup",
 			      "uuid = %s", uuid,
 			      "name = %s", vgname,
 			       NULL);
diff --git a/lib/cache/lvmetad.h b/lib/cache/lvmetad.h
index ce4affa8e..d5f3215bf 100644
--- a/lib/cache/lvmetad.h
+++ b/lib/cache/lvmetad.h
@@ -168,6 +168,7 @@ int lvmetad_pvscan_foreign_vgs(struct cmd_context *cmd, activation_handler handl
 
 int lvmetad_vg_clear_outdated_pvs(struct volume_group *vg);
 void lvmetad_validate_global_cache(struct cmd_context *cmd, int force);
+int lvmetad_token_matches(struct cmd_context *cmd);
 
 int lvmetad_vg_is_foreign(struct cmd_context *cmd, const char *vgname, const char *vgid);
 
@@ -200,6 +201,7 @@ int lvmetad_vg_is_foreign(struct cmd_context *cmd, const char *vgname, const cha
 #    define lvmetad_vg_clear_outdated_pvs(vg)           (1)
 #    define lvmetad_validate_global_cache(cmd, force)	do { } while (0)
 #    define lvmetad_vg_is_foreign(cmd, vgname, vgid) (0)
+#    define lvmetad_token_matches(cmd) (1)
 
 #  endif	/* LVMETAD_SUPPORT */
 
diff --git a/lib/config/config_settings.h b/lib/config/config_settings.h
index 330e22375..5849ac9d1 100644
--- a/lib/config/config_settings.h
+++ b/lib/config/config_settings.h
@@ -854,6 +854,11 @@ cfg(global_use_lvmetad_CFG, "use_lvmetad", global_CFG_SECTION, 0, CFG_TYPE_BOOL,
 	"scanning from the LVM system entirely, including lvmetad, use\n"
 	"devices/global_filter.\n")
 
+cfg(global_lvmetad_update_wait_time_CFG, "lvmetad_update_wait_time", global_CFG_SECTION, CFG_DEFAULT_COMMENTED, CFG_TYPE_INT, DEFAULT_LVMETAD_UPDATE_WAIT_TIME, vsn(2, 2, 142), NULL, 0, NULL,
+	"The number of seconds a command will wait for lvmetad update to finish.\n"
+	"After waiting for this period, a command will not use lvmetad, and\n"
+	"will revert to disk scanning.\n")
+
 cfg(global_use_lvmlockd_CFG, "use_lvmlockd", global_CFG_SECTION, 0, CFG_TYPE_BOOL, 0, vsn(2, 2, 124), NULL, 0, NULL,
 	"Use lvmlockd for locking among hosts using LVM on shared storage.\n"
 	"Applicable only if LVM is compiled with lockd support in which\n"
diff --git a/lib/config/defaults.h b/lib/config/defaults.h
index a6806cda2..5e10ce042 100644
--- a/lib/config/defaults.h
+++ b/lib/config/defaults.h
@@ -52,6 +52,7 @@
 #define DEFAULT_FALLBACK_TO_CLUSTERED_LOCKING 1
 #define DEFAULT_WAIT_FOR_LOCKS 1
 #define DEFAULT_LVMLOCKD_LOCK_RETRIES 3
+#define DEFAULT_LVMETAD_UPDATE_WAIT_TIME 10
 #define DEFAULT_PRIORITISE_WRITE_LOCKS 1
 #define DEFAULT_USE_MLOCKALL 0
 #define DEFAULT_METADATA_READ_ONLY 0
diff --git a/tools/commands.h b/tools/commands.h
index aba5b40b9..f49e57f22 100644
--- a/tools/commands.h
+++ b/tools/commands.h
@@ -698,7 +698,7 @@ xx(lvs,
 
 xx(lvscan,
    "List all logical volumes in all volume groups",
-   PERMITTED_READ_ONLY | ALL_VGS_IS_DEFAULT | LOCKD_VG_SH,
+   PERMITTED_READ_ONLY | ALL_VGS_IS_DEFAULT | LOCKD_VG_SH | NO_LVMETAD_AUTOSCAN,
    "lvscan\n"
    "\t[-a|--all]\n"
    "\t[-b|--blockdevice]\n"
@@ -971,7 +971,7 @@ xx(pvs,
 
 xx(pvscan,
    "List all physical volumes",
-   PERMITTED_READ_ONLY | LOCKD_VG_SH,
+   PERMITTED_READ_ONLY | LOCKD_VG_SH | NO_LVMETAD_AUTOSCAN,
    "pvscan\n"
    "\t[-b|--background]\n"
    "\t[--cache [-a|--activate ay] [ DevicePath | -j|--major major --minor minor]...]\n"
@@ -1243,7 +1243,7 @@ xx(vgextend,
 
 xx(vgimport,
    "Register exported volume group with system",
-   ALL_VGS_IS_DEFAULT,
+   ALL_VGS_IS_DEFAULT | NO_LVMETAD_AUTOSCAN,
    "vgimport\n"
    "\t[-a|--all]\n"
    "\t[--commandprofile ProfileName]\n"
@@ -1382,7 +1382,7 @@ xx(vgs,
 
 xx(vgscan,
    "Search for all volume groups",
-   PERMITTED_READ_ONLY | ALL_VGS_IS_DEFAULT | LOCKD_VG_SH,
+   PERMITTED_READ_ONLY | ALL_VGS_IS_DEFAULT | LOCKD_VG_SH | NO_LVMETAD_AUTOSCAN,
    "vgscan "
    "\t[--cache]\n"
    "\t[--commandprofile ProfileName]\n"
diff --git a/tools/lvmcmdline.c b/tools/lvmcmdline.c
index 2ee54e8ff..0a286d8eb 100644
--- a/tools/lvmcmdline.c
+++ b/tools/lvmcmdline.c
@@ -1643,13 +1643,26 @@ int lvm_run_command(struct cmd_context *cmd, int argc, char **argv)
 	}
 
 	/*
-	 * Other hosts might have changed foreign VGs so enforce a rescan
-	 * before processing any command using them.
+	 * pvscan/vgscan/lvscan/vgimport want their own control over rescanning
+	 * to populate lvmetad and have similar code of their own.
+	 * Other commands use this general policy for using lvmetad.
+	 *
+	 * The lvmetad cache may need to be repopulated before we use it because:
+	 * - We are reading foreign VGs which others hosts may have changed
+	 *   which our lvmetad would not have seen.
+	 * - lvmetad may have just been started and no command has been run
+	 *   to populate it yet (e.g. no pvscan --cache was run).
+	 * - Another local command may have run with a different global filter
+	 *   which changed the content of lvmetad from what we want (recognized
+	 *   by different token values.)
 	 */
-	if (cmd->include_foreign_vgs && lvmetad_used() &&
-	    !lvmetad_pvscan_foreign_vgs(cmd, NULL)) {
-		log_error("Failed to scan devices.");
-		return ECMD_FAILED;
+	if (lvmetad_used() && !(cmd->command->flags & NO_LVMETAD_AUTOSCAN)) {
+		if (!lvmetad_token_matches(cmd) || cmd->include_foreign_vgs) {
+			if (lvmetad_used() && !lvmetad_pvscan_all_devs(cmd, NULL)) {
+				log_warn("WARNING: Not using lvmetad because device scan failed.");
+				lvmetad_set_active(cmd, 0);
+			}
+		}
 	}
 
 	/*
diff --git a/tools/lvscan.c b/tools/lvscan.c
index 751ecb6d7..2e557308c 100644
--- a/tools/lvscan.c
+++ b/tools/lvscan.c
@@ -21,10 +21,8 @@ static int _lvscan_single_lvmetad(struct cmd_context *cmd, struct logical_volume
 	struct dm_list all_pvs;
 	char pvid_s[64] __attribute__((aligned(8)));
 
-	if (!lvmetad_used()) {
-		log_verbose("Ignoring lvscan --cache because lvmetad is not in use.");
+	if (!lvmetad_used())
 		return ECMD_PROCESSED;
-	}
 
 	dm_list_init(&all_pvs);
 
@@ -98,6 +96,24 @@ int lvscan(struct cmd_context *cmd, int argc, char **argv)
 		return EINVALID_CMD_LINE;
 	}
 
+	if (!lvmetad_used() && arg_is_set(cmd, cache_long_ARG))
+		log_verbose("Ignoring lvscan --cache because lvmetad is not in use.");
+
+	/* Needed because this command has NO_LVMETAD_AUTOSCAN. */
+	if (lvmetad_used() && !lvmetad_token_matches(cmd)) {
+		log_print_unless_silent("Scanning all devices.");
+
+		if (lvmetad_used() && !lvmetad_pvscan_all_devs(cmd, NULL)) {
+			log_warn("WARNING: Not using lvmetad because device scan failed.");
+			lvmetad_set_active(cmd, 0);
+		}
+
+		/*
+		 * FIXME: doing lvscan --cache after a full scan is pointless.
+		 * Should the cache case just exit here?
+		 */
+	}
+
 	return process_each_lv(cmd, argc, argv, 0, NULL,
 			       &lvscan_single);
 }
diff --git a/tools/pvscan.c b/tools/pvscan.c
index b224c30b0..e9826fe30 100644
--- a/tools/pvscan.c
+++ b/tools/pvscan.c
@@ -234,8 +234,6 @@ static int _pvscan_lvmetad(struct cmd_context *cmd, int argc, char **argv)
 	dev_t devno;
 	activation_handler handler = NULL;
 
-	cmd->include_foreign_vgs = 1;
-
 	/*
 	 * Return here immediately if lvmetad is not used.
 	 * Also return if locking_type=3 (clustered) as we
@@ -273,11 +271,29 @@ static int _pvscan_lvmetad(struct cmd_context *cmd, int argc, char **argv)
 
 	/* Scan everything? */
 	if (!argc && !devno_args) {
-		if (!lvmetad_pvscan_all_devs(cmd, handler))
+		if (!lvmetad_pvscan_all_devs(cmd, handler)) {
+			log_error("Failed to scan devices.");
 			ret = ECMD_FAILED;
+		}
 		goto out;
 	}
 
+	/*
+	 * FIXME: when specific devs are named, we generally don't
+	 * want to scan any other devs, but if lvmetad is not yet
+	 * populated, the first 'pvscan --cache dev' does need to
+	 * do a full scan.  We want to remove the need for this
+	 * case so that 'pvscan --cache dev' is guaranteed to never
+	 * scan any devices other than those specified.
+	 */
+	if (lvmetad_used() && !lvmetad_token_matches(cmd)) {
+		if (lvmetad_used() && !lvmetad_pvscan_all_devs(cmd, NULL)) {
+			log_error("Failed to scan devices.");
+			ret = ECMD_FAILED;
+			goto out;
+		}
+	}
+
 	log_verbose("Using physical volume(s) on command line");
 
 	/* Process any command line PVs first. */
@@ -404,6 +420,16 @@ int pvscan(struct cmd_context *cmd, int argc, char **argv)
 			  arg_count(cmd, exported_ARG) ?
 			  "of exported volume group(s)" : "in no volume group");
 
+	/* Needed because this command has NO_LVMETAD_AUTOSCAN. */
+	if (lvmetad_used() && !lvmetad_token_matches(cmd)) {
+		log_print_unless_silent("Scanning all devices.");
+
+		if (lvmetad_used() && !lvmetad_pvscan_all_devs(cmd, NULL)) {
+			log_warn("WARNING: Not using lvmetad because device scan failed.");
+			lvmetad_set_active(cmd, 0);
+		}
+	}
+
 	if (!lock_vol(cmd, VG_GLOBAL, LCK_VG_WRITE, NULL)) {
 		log_error("Unable to obtain global lock.");
 		return ECMD_FAILED;
diff --git a/tools/tools.h b/tools/tools.h
index 3762e8eed..7b1bda3a0 100644
--- a/tools/tools.h
+++ b/tools/tools.h
@@ -110,6 +110,8 @@ struct arg_value_group_list {
 #define REQUIRES_FULL_LABEL_SCAN 0x00000080
 /* Command must use all specified arg names and fail if all cannot be used. */
 #define MUST_USE_ALL_ARGS        0x00000100
+/* Command wants to control the device scan for lvmetad itself. */
+#define NO_LVMETAD_AUTOSCAN      0x00000200
  
 /* a register of the lvm commands */
 struct command {
diff --git a/tools/vgimport.c b/tools/vgimport.c
index caeaf09cf..ce693983c 100644
--- a/tools/vgimport.c
+++ b/tools/vgimport.c
@@ -93,9 +93,11 @@ int vgimport(struct cmd_context *cmd, int argc, char **argv)
 	 * We need to reread it to see that it's been exported before we can
 	 * import it.
 	 */
-	if (lvmetad_active() && !lvmetad_pvscan_all_devs(cmd, NULL)) {
-		log_error("Failed to scan devices.");
-		return ECMD_FAILED;
+	if (lvmetad_used()) {
+		if (!lvmetad_pvscan_all_devs(cmd, NULL)) {
+			log_warn("WARNING: Not using lvmetad because device scan failed.");
+			lvmetad_set_active(cmd, 0);
+		}
 	}
 
 	return process_each_vg(cmd, argc, argv, NULL,
diff --git a/tools/vgscan.c b/tools/vgscan.c
index a5b04a33f..63dd47390 100644
--- a/tools/vgscan.c
+++ b/tools/vgscan.c
@@ -61,21 +61,22 @@ int vgscan(struct cmd_context *cmd, int argc, char **argv)
 		cmd->filter->wipe(cmd->filter);
 	lvmcache_destroy(cmd, 1, 0);
 
-	if (arg_count(cmd, cache_long_ARG)) {
-		cmd->include_foreign_vgs = 1;
+	if (!lvmetad_used() && arg_is_set(cmd, cache_long_ARG))
+		log_verbose("Ignoring vgscan --cache command because lvmetad is not in use.");
 
-		if (lvmetad_active()) {
-			if (!lvmetad_pvscan_all_devs(cmd, NULL))
-				return ECMD_FAILED;
-		}
-		else {
-			log_error("Cannot proceed since lvmetad is not active.");
-			unlock_vg(cmd, VG_GLOBAL);
-			return ECMD_FAILED;
+	if (lvmetad_used() && (arg_is_set(cmd, cache_long_ARG) || !lvmetad_token_matches(cmd))) {
+		log_print_unless_silent("Scanning all devices.");
+
+		if (lvmetad_used() && !lvmetad_pvscan_all_devs(cmd, NULL)) {
+			log_warn("WARNING: Not using lvmetad because device scan failed.");
+			lvmetad_set_active(cmd, 0);
 		}
 	}
 
-	log_print_unless_silent("Reading all physical volumes.  This may take a while...");
+	if (!lvmetad_used())
+		log_print_unless_silent("Reading all physical volumes.  This may take a while...");
+	else
+		log_print_unless_silent("Reading volume groups from cache.");
 
 	maxret = process_each_vg(cmd, argc, argv, NULL, 0, NULL,
 				 &vgscan_single);