Add lock-file functionality for qvm-template install.

qubesadmin/tools/qvm_template.py

@@ -25,6 +25,7 @@ TEMP_DIR = '/var/tmp'
 PACKAGE_NAME_PREFIX = 'qubes-template-'
 CACHE_DIR = os.path.join(xdg.BaseDirectory.xdg_cache_home, 'qvm-template')
 UNVERIFIED_SUFFIX = '.unverified'
+LOCK_FILE = '/var/tmp/qvm-template.lck'
 
 def qubes_release():
     if os.path.exists('/usr/share/qubes/marker-vm'):
@@ -142,7 +143,15 @@ def parse_config(path):
 
 def install(args, app, version_selector=VersionSelector.LATEST,
         ignore_existing=False):
-    # TODO: Lock, mentioned in the note above
+    try:
+        with open(LOCK_FILE, 'x') as _:
+            pass
+    except FileExistsError:
+        parser.error(('%s already exists.'
+            ' Perhaps another instance of qvm-template is running?')
+            % LOCK_FILE)
+
+    try:
         transaction_set = rpm.TransactionSet()
 
         rpm_list = []
@@ -200,7 +209,8 @@ def install(args, app, version_selector=VersionSelector.LATEST,
                 # Another check for already-downloaded RPMs
                 if not ignore_existing and name in app.domains:
                     print(('Template \'%s\' already installed, skipping...'
-                    ' (You may want to use the {reinstall,upgrade,downgrade}'
+                        ' (You may want to use the'
+                        ' {reinstall,upgrade,downgrade}'
                         ' operations.)') % name, file=sys.stderr)
                     continue
 
@@ -233,6 +243,8 @@ def install(args, app, version_selector=VersionSelector.LATEST,
                 tpl.features['template-reponame'] = reponame
                 tpl.features['template-summary'] = \
                     package_hdr[rpm.RPMTAG_SUMMARY]
+    finally:
+        os.remove(LOCK_FILE)
 
 def qrexec_popen(args, app, service, stdout=subprocess.PIPE, filter_esc=True):
     if args.updatevm: