add config option 'manual_cache_clean'.

This option allows user to specify manual cleaning of the
/var/lib/cloud/instance/ link, for a data source that might not be present on
every boot.

4 files changed, 20 insertions, 3 deletions

diff --git a/ChangeLog b/ChangeLog
index 7daf418e..80bb4d12 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -10,6 +10,9 @@
  - turn resize_rootfs default to True
  - avoid mounts in DataSourceOVF if 'read' on device fails
    'mount /dev/sr0' for an empty virtual cdrom device was taking 18 seconds
+ - add 'manual_cache_clean' option to select manual cleaning of
+   the /var/lib/cloud/instance/ link, for a data source that might
+   not be present on every boot
 0.6.0:
  - change permissions of /var/log/cloud-init.log to accomodate
    syslog writing to it (LP: #704509)
diff --git a/cloud-init.py b/cloud-init.py
index c9c03b3f..e8454eaa 100755
--- a/cloud-init.py
+++ b/cloud-init.py
@@ -93,7 +93,10 @@ def main():
     # but we want 'start' to benefit from a cache if
     # a previous start-local populated one
     if cmd == "start-local":
-        cloudinit.purge_cache()
+        manclean = util.get_cfg_option_bool(cfg, 'manual_cache_clean',False)
+        if manclean:
+            log.debug("not purging cache, manual_cache_clean = True")
+        cloudinit.purge_cache(not manclean)
 
     cloud = cloudinit.CloudInit(ds_deps=deps[cmd])
 
diff --git a/cloudinit/__init__.py b/cloudinit/__init__.py
index 99cc4d46..02147461 100644
--- a/cloudinit/__init__.py
+++ b/cloudinit/__init__.py
@@ -501,8 +501,9 @@ def initfs():
         if g == "-1" or g == "None": g = None
         util.chownbyname(log_file, u, g)
 
-def purge_cache():
-    rmlist = ( boot_finished , cur_instance_link )
+def purge_cache(rmcur=True):
+    rmlist = [ boot_finished ]
+    if rmcur: rmlist.append(cur_instance_link)
     for f in rmlist:
         try:
             os.unlink(f)
diff --git a/doc/examples/cloud-config.txt b/doc/examples/cloud-config.txt
index 0a1d4279..8d47234d 100644
--- a/doc/examples/cloud-config.txt
+++ b/doc/examples/cloud-config.txt
@@ -383,3 +383,13 @@ syslog_fix_perms: syslog:root
 password: passw0rd
 chpasswd: { expire: False }
 ssh_pwauth: True
+
+# manual cache clean.
+#  By default, the link from /var/lib/cloud/instance to
+#  the specific instance in /var/lib/cloud/instances/ is removed on every
+#  boot.  The cloud-init code then searches for a DataSource on every boot
+#  if your DataSource will not be present on every boot, then you can set
+#  this option to 'True', and maintain (remove) that link before the image
+#  will be booted as a new instance.
+# default is False
+manual_cache_clean = False