hints: invalidate when pvscan --cache sees a new PV

An idea from Zdenek for better ensuring valid hints by invalidating
them when pvscan --cache <device> sees a new PV, which is a case
where we know that hints should be invalidated.  This is triggered
from systemd/udev logic, and there may be some cases where it would
invalidate hints that the existing methods wouldn't detect.

lib/label/hints.c

@@ -1025,6 +1025,21 @@ void clear_hint_file(struct cmd_context *cmd)
 		stack;
 }
 
+/*
+ * This is used when pvscan --cache sees a new PV, which
+ * means we should refresh hints.  It could catch some case
+ * which the other methods of detecting stale hints may miss.
+ */
+void invalidate_hints(struct cmd_context *cmd)
+{
+	/* No commands are using hints. */
+	if (!cmd->enable_hints)
+		return;
+
+	if (!_touch_newhints())
+		stack;
+}
+
 /*
  * Currently, all the commands using hints (ALLOW_HINTS) take an optional or
  * required first position arg of a VG name or LV name.  If some other command

lib/label/hints.h

@@ -28,6 +28,8 @@ int write_hint_file(struct cmd_context *cmd, int newhints);
 
 void clear_hint_file(struct cmd_context *cmd);
 
+void invalidate_hints(struct cmd_context *cmd);
+
 int get_hints(struct cmd_context *cmd, struct dm_list *hints, int *newhints,
               struct dm_list *devs_in, struct dm_list *devs_out);
 

test/shell/hints.sh

@@ -273,11 +273,12 @@ diff $HINTS $PREV
 #
 
 # pvs (no change), pvscan (hints are new), pvs (no change)
+rm $HINTS $PREV
 pvs
 cp $HINTS $PREV
-diff $HINTS $PREV
-cp $HINTS $PREV
+# this next pvscan recreates the hints file
 pvscan --cache
+# the only diff will be "Created by pvscan ..." vs "Created by pvs ..."
 not diff $HINTS $PREV
 cp $HINTS $PREV
 pvs
@@ -285,6 +286,8 @@ diff $HINTS $PREV
 grep 'Created by pvscan' $HINTS
 # dev4 is a PV not used by a VG, dev5 is not a PV
 # using dd to copy skirts hint tracking so dev5 won't be seen
+# (unless the dd triggers udev which triggers pvscan --cache $dev5,
+# but I've not seen that happen in tests so far.)
 dd if="$dev4" of="$dev5" bs=1M
 # this pvs won't see dev5
 pvs > foo
@@ -314,6 +317,22 @@ not grep "$dev5" foo
 grep "$dev4" $HINTS
 not grep "$dev5" $HINTS
 
+#
+# Test pvscan --cache <dev> forces refresh
+#
+
+rm $HINTS $PREV
+pvs
+cp $HINTS $PREV
+# this next pvscan creates newhints to trigger a refresh
+pvscan --cache "$dev5"
+cat $NEWHINTS
+# this next pvs creates new hints
+pvs
+# the only diff will be "Created by..."
+not diff $HINTS $PREV
+
+
 
 #
 # Test incorrect dev-to-pvid info in hints is detected

tools/pvscan.c

@@ -17,6 +17,7 @@
 
 #include "lib/cache/lvmcache.h"
 #include "lib/metadata/metadata.h"
+#include "lib/label/hints.h"
 
 #include <dirent.h>
 
@@ -632,6 +633,7 @@ int pvscan_cache_cmd(struct cmd_context *cmd, int argc, char **argv)
 	int do_activate = arg_is_set(cmd, activate_ARG);
 	int all_vgs = 0;
 	int add_errors = 0;
+	int add_single_count = 0;
 	int ret = ECMD_PROCESSED;
 
 	dm_list_init(&single_devs);
@@ -750,6 +752,8 @@ int pvscan_cache_cmd(struct cmd_context *cmd, int argc, char **argv)
 			if (dev->flags & DEV_FILTER_OUT_SCAN)
 				continue;
 
+			add_single_count++;
+
 			/*
 			 * Devices that exist and pass the lvmetad filter
 			 * are online.
@@ -801,6 +805,8 @@ int pvscan_cache_cmd(struct cmd_context *cmd, int argc, char **argv)
 			if (dev->flags & DEV_FILTER_OUT_SCAN)
 				continue;
 
+			add_single_count++;
+
 			/*
 			 * Devices that exist and pass the lvmetad filter
 			 * are online.
@@ -811,6 +817,16 @@ int pvscan_cache_cmd(struct cmd_context *cmd, int argc, char **argv)
 	}
 
 activate:
+	/*
+	 * When a new PV appears, the system runs pvscan --cache dev.
+	 * This also means that existing hints are invalid, and
+	 * we can force hints to be refreshed here.  There may be
+	 * cases where this detects a change that the other methods
+	 * of detecting invalid hints doesn't catch.
+	 */
+	if (add_single_count)
+		invalidate_hints(cmd);
+
 	/*
 	 * Special case: pvscan --cache -aay dev 
 	 * where dev has no VG metadata, and it's the final device to