xen init script: Do nothing if running for wrong Xen package

See the big comment.  We think that this is responsible for various
bugs and, particularly, reports of mysteriously missing xenconsoled.

For example, this bug would mean that after a Xen version upgrade,
autoremoval of an obsolete xen-utils-V package would stop the running
xenconsoled.  This is obviously awkward to track down, and could occur
many weeks or months after the upgrade.

Closes: #851654
Signed-off-by: Ian Jackson <ian.jackson@citrix.com>
Acked-by: Hans van Kranenburg <hans@knorrie.org>

diff --git a/debian/xen-utils-common.xen.init b/debian/xen-utils-common.xen.init
index da7d361453102341e0bd577c25c8e243dcc22d7d..b0df7be8abe62c3255f53af1a8c76aa93b653d60 100644 (file)
--- a/debian/xen-utils-common.xen.init
+++ b/debian/xen-utils-common.xen.init
@@ -24,6 +24,35 @@ case "$(cat /sys/hypervisor/type 2>/dev/null)" in
 xen)           ;;
 *)     exit 0  ;; # not running under Xen
 esac
+
+VERSION=$(/usr/lib/xen-common/bin/xen-version)
+
+# The arrangements for the `xen' init script are a bit odd.
+# This script is part of xen-utils-common, of which there is one
+# version installed regardless of the Xen version.
+#
+# But it is called by the prerm and postinsts of xen-utils-VERSION.
+# The idea is that (for example) if xen-utils-VERSION is upgraded, the
+# daemons are restarted.
+#
+# However, this means that this script may be called by the
+# maintscript of a xen-utils-V package for a different V to the
+# running version of Xen (X, say).  Such a xen-utils-V package does
+# not actually want to start or stop its daemons.  Indeed, the version
+# selection machinery would redirect its efforts to the xen-utils-X
+# utilities.  But this is not right: we don't actually want to (for
+# example) stop xenconsoled from xen-utils-X just because some
+# not-currently-relevant xen-utils-V is installed/removed/whatever.
+#
+# So we use DPKG_MAINTSCRIPT_PACKAGE to detect this situation, and
+# turn these extraneous calls into no-ops.
+
+case $DPKG_MAINTSCRIPT_PACKAGE in
+xen-utils-$VERSION)    ;;      # xen-utils-V maintscript, under Xen X=V
+xen-utils-*)           exit 0;; # xen-utils-V maintscript, but under Xen X!=V
+*)                     ;;      # maybe not under dpkg, etc.
+esac
+
 ROOT=$(/usr/lib/xen-common/bin/xen-dir 2>/dev/null)
 if [ $? -ne 0 ]; then
        log_warning_msg "Not running within Xen or no compatible utils"