From: Evan Broder <broder@mit.edu>
Date: Mon, 10 Nov 2008 08:16:05 +0000 (-0500)
Subject: Use a lock LV when starting sysvms since exclusive LV activation has
X-Git-Tag: 0.0.13^0
X-Git-Url: http://xvm.mit.edu/gitweb/invirt/packages/invirt-xen-config.git/commitdiff_plain/8f57a1411c5cec075f3e81eb58fe0d2e471bb1f7?hp=70660d7da71a10f52d18c31a08874c3e695710a3

Use a lock LV when starting sysvms since exclusive LV activation has
useless semantics

svn path=/trunk/packages/invirt-xen-config/; revision=1580
---

diff --git a/debian/changelog b/debian/changelog
index af7421c..67ae9e7 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,10 @@
+invirt-xen-config (0.0.13) unstable; urgency=low
+
+  * Use a lock LV when attempting to start sysvms since exclusive LV
+    activation has useless semantics
+
+ -- Evan Broder <broder@mit.edu>  Mon, 10 Nov 2008 03:15:31 -0500
+
 invirt-xen-config (0.0.12) unstable; urgency=low
 
   * Add missing close paren to init script
diff --git a/debian/invirt-xen-config.init b/debian/invirt-xen-config.init
index 430ae9e..d0d8582 100755
--- a/debian/invirt-xen-config.init
+++ b/debian/invirt-xen-config.init
@@ -26,31 +26,39 @@ start_sysvm() {
     # somewhere on the cluster
     
     VM="$1"
-    DISK="/dev/xenvg/${VM}_hda"
+    LV="${VM}_hda"
+    DISK="/dev/xenvg/$LV"
     
     # Don't bother trying to start the VM if it's already running
-    if xm list "$1" >/dev/null 2>&1; then
+    if xm list "$VM" >/dev/null 2>&1; then
         return 1
     fi
     
-    if lvchange -a n "$DISK" >/dev/null 2>&1 && lvchange -a ey "$DISK" >/dev/null 2>&1; then
-        # If we can disable and then re-enable the VMs disk, then the
-        # VM can't be running. If the lvchange -a ey succeeds, then we
-        # have an exclusive lock across the cluster on enabling the
-        # disk, which avoids the potential race condition of two hosts
-        # starting a VM at the same time
-        [ "$VERBOSE" != no ] && log_daemon_msg "Starting sysvm $VM"
-        xm create "sysvms/$VM" >/dev/null
-        [ "$VERBOSE" != no ] && log_end_msg $?
-        RET=0
-    else
-        RET=1
-    fi
+    RET=1
+    # To keep multiple hosts from trying to start a VM at the same
+    # time, lock VM creation at startup-time with a lock LV, since LV
+    # creation is atomic
+    if lvcreate -L 1K -n "lock_${LV}" xenvg >/dev/null 2>&1; then
+        # If we can disable the LV, then the VM isn't already running
+        # somewhere else
+        if lvchange -a n "$DISK" >/dev/null 2>&1; then
+            lvchange -a y "$DISK" >/dev/null 2>&1
+            
+            [ "$VERBOSE" != no ] && log_daemon_msg "Starting sysvm $VM"
+            xm create "sysvms/$VM" >/dev/null
+            [ "$VERBOSE" != no ] && log_end_msg $?
+            RET=0
+        fi
+        
+        # Regardless of whether we could get the lock or not, the
+        # lvchange -a n probably disabled the LV somewhere; be sure we
+        # clean up
+        lvchange -a y "$DISK" >/dev/null 2>&1
     
-    # Regardless of whether we could get the lock or not, the
-    # lvchange -a n probably disabled the LV somewhere; be sure we
-    # clean up
-    lvchange -a y "$DISK" >/dev/null 2>&1
+        # Cleanup the lock, regardless of whether we started the LV
+        lvchange -a n "/dev/xenvg/lock_${LV}"
+        lvremove -f "/dev/xenvg/lock_${LV}"
+    fi
     
     return $RET
 }