tests: add a test for reverting reshapes

Only reverting reshapes that grow the array so far.

Signed-off-by: NeilBrown <neilb@suse.de>

test

@@ -95,6 +95,7 @@ do_setup() {
     eval dev$d=/dev/loop$d
     eval file$d=$targetdir/mdtest$d
     eval devlist=\"\$devlist \$dev$d\"
+    eval devlist$d=\"\$devlist\"
    #" <-- add this quote to un-confuse vim syntax highlighting
   done
   path0=$dev6

tests/07revert-grow

@@ -0,0 +1,43 @@
+set -e -x
+
+# revert a reshape that is increasing the number of devices,
+# raid5, raid6, and raid10
+
+# RAID5
+mdadm -CR --assume-clean $md0 -l5 -n4 -x1 $devlist4
+check raid5
+testdev $md0 3 $mdsize1 512
+mdadm -G $md0 -n 5
+sleep 3
+mdadm -S $md0
+mdadm -A $md0 --update=revert-reshape $devlist4 --backup-file=/tmp/md-backup
+check wait
+check raid5
+testdev $md0 3 $mdsize1 512
+mdadm -S $md0
+
+# RAID6
+mdadm -CR --assume-clean $md0 -l6 -n4 -x1 $devlist4
+check raid6
+testdev $md0 2 $mdsize1 512
+mdadm -G $md0 -n 5
+sleep 3
+mdadm -S $md0
+mdadm -A $md0 --update=revert-reshape $devlist4 --backup-file=/tmp/md-backup
+check wait
+check raid6
+testdev $md0 2 $mdsize1 512
+mdadm -S $md0
+
+# RAID10
+mdadm -CR --assume-clean $md0 -l10 -n4 -x1 $devlist4
+check raid10
+testdev $md0 2 $mdsize1 512
+mdadm -G $md0 -n 5
+sleep 3
+mdadm -S $md0
+strace -o /tmp/str ./mdadm -A $md0 --update=revert-reshape $devlist4
+check wait
+check raid10
+testdev $md0 2 $mdsize1 512
+mdadm -S $md0