Changeset 1580

Timestamp:

Nov 10, 2008, 3:16:05 AM (16 years ago)

Author:

broder

Message:

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

Location:

trunk/packages/invirt-xen-config/debian

Files:

• changelog (modified) (1 diff)
• invirt-xen-config.init (modified) (1 diff)

trunk/packages/invirt-xen-config/debian/changelog

@@ +1 @@
+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
 

trunk/packages/invirt-xen-config/debian/invirt-xen-config.init

@@ -27 +27 @@
     
     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 $?
-        RET=0
-    else
-        RET=1
+    RET=1
+    # To keep multiple hosts from trying to start a VM at the same
+    # time, lock VM creation at startup-time with a lock LV, since LV
+    # creation is atomic
+    if lvcreate -L 1K -n "lock_${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
+    
+        # Cleanup the lock, regardless of whether we started the LV
+        lvchange -a n "/dev/xenvg/lock_${LV}"
+        lvremove -f "/dev/xenvg/lock_${LV}"
     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
     
     return $RET