Fix check-mode incorrectly returning changed (#2220)

The lvol module has a different logic in check-mode for knowing when a change is induced. And this logic is *only* based on a size check. However during a normal run, it is the lvreduce or lvextend tool that decides when a change is performed (or when the requested and existing sizes differ). So while in check-mode the module reports a change, in real run-mode it does not in fact changes anything an reports ok.

One solution would be to implement the exact size-comparison logic that is implemented in lvextend and lvreduce, but we opted to use the `--test` option to each command to verify if a change is induced or not. In effect both check-mode and run-mode use the exact same logic and conclusion.

system/lvol.py

@@ -214,6 +214,12 @@ def main():
     if opts is None:
         opts = ""
 
+    # Add --test option when running in check-mode
+    if module.check_mode:
+        test_opt = ' --test'
+    else:
+        test_opt = ''
+
     if size:
         # LVCREATE(8) -l --extents option with percentage
         if '%' in size:
@@ -297,14 +303,11 @@ def main():
     if this_lv is None:
         if state == 'present':
             ### create LV
-            if module.check_mode:
-                changed = True
-            else:
             lvcreate_cmd = module.get_bin_path("lvcreate", required=True)
             if snapshot is not None:
-                    cmd = "%s %s -%s %s%s -s -n %s %s %s/%s" % (lvcreate_cmd, yesopt, size_opt, size, size_unit, snapshot, opts, vg, lv)
+                cmd = "%s %s %s -%s %s%s -s -n %s %s %s/%s" % (lvcreate_cmd, test_opt, yesopt, size_opt, size, size_unit, snapshot, opts, vg, lv)
             else:
-                    cmd = "%s %s -n %s -%s %s%s %s %s %s" % (lvcreate_cmd, yesopt, lv, size_opt, size, size_unit, opts, vg, pvs)
+                cmd = "%s %s %s -n %s -%s %s%s %s %s %s" % (lvcreate_cmd, test_opt, yesopt, lv, size_opt, size, size_unit, opts, vg, pvs)
             rc, _, err = module.run_command(cmd)
             if rc == 0:
                 changed = True
@@ -313,12 +316,10 @@ def main():
     else:
         if state == 'absent':
             ### remove LV
-            if module.check_mode:
-                module.exit_json(changed=True)
             if not force:
                 module.fail_json(msg="Sorry, no removal of logical volume %s without force=yes." % (this_lv['name']))
             lvremove_cmd = module.get_bin_path("lvremove", required=True)
-            rc, _, err = module.run_command("%s --force %s/%s" % (lvremove_cmd, vg, this_lv['name']))
+            rc, _, err = module.run_command("%s %s --force %s/%s" % (lvremove_cmd, test_opt, vg, this_lv['name']))
             if rc == 0:
                 module.exit_json(changed=True)
             else:
@@ -349,10 +350,7 @@ def main():
                     tool = '%s %s' % (tool, '--force')
 
             if tool:
-                if module.check_mode:
+                cmd = "%s %s -%s %s%s %s/%s %s" % (tool, test_opt, size_opt, size, size_unit, vg, this_lv['name'], pvs)
-                    changed = True
-                else:
-                    cmd = "%s -%s %s%s %s/%s %s" % (tool, size_opt, size, size_unit, vg, this_lv['name'], pvs)
                 rc, out, err = module.run_command(cmd)
                 if "Reached maximum COW size" in out:
                     module.fail_json(msg="Unable to resize %s to %s%s" % (lv, size, size_unit), rc=rc, err=err, out=out)
@@ -361,6 +359,8 @@ def main():
                     msg="Volume %s resized to %s%s" % (this_lv['name'], size_requested, unit)
                 elif "matches existing size" in err:
                     module.exit_json(changed=False, vg=vg, lv=this_lv['name'], size=this_lv['size'])
+                elif "not larger than existing size" in err:
+                    module.exit_json(changed=False, vg=vg, lv=this_lv['name'], size=this_lv['size'], msg="Original size is larger than requested size", err=err)
                 else:
                     module.fail_json(msg="Unable to resize %s to %s%s" % (lv, size, size_unit), rc=rc, err=err)
 
@@ -379,10 +379,7 @@ def main():
                     tool = '%s %s' % (tool, '--force')
 
             if tool:
-                if module.check_mode:
+                cmd = "%s %s -%s %s%s %s/%s %s" % (tool, test_opt, size_opt, size, size_unit, vg, this_lv['name'], pvs)
-                    changed = True
-                else:
-                    cmd = "%s -%s %s%s %s/%s %s" % (tool, size_opt, size, size_unit, vg, this_lv['name'], pvs)
                 rc, out, err = module.run_command(cmd)
                 if "Reached maximum COW size" in out:
                     module.fail_json(msg="Unable to resize %s to %s%s" % (lv, size, size_unit), rc=rc, err=err, out=out)
@@ -390,6 +387,8 @@ def main():
                     changed = True
                 elif "matches existing size" in err:
                     module.exit_json(changed=False, vg=vg, lv=this_lv['name'], size=this_lv['size'])
+                elif "not larger than existing size" in err:
+                    module.exit_json(changed=False, vg=vg, lv=this_lv['name'], size=this_lv['size'], msg="Original size is larger than requested size", err=err)
                 else:
                     module.fail_json(msg="Unable to resize %s to %s%s" % (lv, size, size_unit), rc=rc, err=err)