Disallow the addition of mirror images while a mirror up-convert

is already occurring.  The addition of new legs can be retried
once the current conversion is complete.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.64 -
 =================================
+  Disallow the addition of mirror images while a conversion is happening.
   Disallow primary mirror image removal when mirror is not in-sync.
   Remove obsolete --name parameter from vgcfgrestore.
   Add -S command to clvmd to restart the daemon preserving exclusive locks.

test/t-mirror-lvconvert.sh

@@ -155,11 +155,14 @@ check_and_cleanup_lvs_
 # add 1 mirror
 prepare_lvs_
 lvs -a -o+devices $vg
-lvcreate -l2 -m1 -n $lv1 $vg $dev1 $dev2 $dev3:0
+lvcreate -l5 -m1 -n $lv1 $vg $dev1 $dev2 $dev3:0
 lvs -a -o+devices $vg
 check_mirror_count_ $vg/$lv1 2
 check_mirror_log_ $vg/$lv1
-lvconvert -m+1 -i1 $vg/$lv1 $dev4
+lvconvert -m+1 -i 20 -b $vg/$lv1 $dev4
+# Next convert should fail b/c we can't have 2 at once
+not lvconvert -m+1 -b $vg/$lv1 $dev5
+wait_conversion_ $vg/$lv1
 lvs -a -o+devices $vg
 check_no_tmplvs_ $vg/$lv1
 check_mirror_count_ $vg/$lv1 3

tools/lvconvert.c

@@ -994,6 +994,16 @@ static int _lvconvert_mirrors_aux(struct cmd_context *cmd,
 			return 0;
 		}
 
+		/*
+		 * Is there already a convert in progress?  We do not
+		 * currently allow more than one.
+		 */
+		if (find_temporary_mirror(lv) || (lv->status & CONVERTING)) {
+			log_error("%s is already being converted.  Unable to start another conversion.",
+				  lv->name);
+			return 0;
+		}
+
 		/*
 		 * Log addition/removal should be done before the layer
 		 * insertion to make the end result consistent with