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.

1 files changed, 5 insertions, 3 deletions

diff --git a/tools/vgimport.c b/tools/vgimport.c
index caeaf09cf..3c08876f0 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, 1)) {
+			log_warn("WARNING: Not using lvmetad because cache update failed.");
+			lvmetad_set_active(cmd, 0);
+		}
 	}
 
 	return process_each_vg(cmd, argc, argv, NULL,