From: Evan Broder <broder@mit.edu>
Date: Fri, 31 Oct 2008 18:00:19 +0000 (-0400)
Subject: Add some additional documentation on how the sysvm disk locking works
X-Git-Tag: 0.0.13~2
X-Git-Url: http://xvm.mit.edu/gitweb/invirt/packages/invirt-xen-config.git/commitdiff_plain/84cdb5b95b921725f369b5b0a5588a606aab96cc?hp=12eb632cfa17518f14e7e8090536fef103bc4982

Add some additional documentation on how the sysvm disk locking works

svn path=/trunk/packages/invirt-xen-config/; revision=1462
---

diff --git a/debian/invirt-xen-config.init b/debian/invirt-xen-config.init
index 02dedc1..ec23d0d 100755
--- a/debian/invirt-xen-config.init
+++ b/debian/invirt-xen-config.init
@@ -39,7 +39,11 @@ start_sysvm() {
     fi
     
     if lvchange -a n "$DISK" >/dev/null 2>&1 && lvchange -a ey "$DISK" >/dev/null 2>&1; then
-        # If we can lock on the VM's disk, then the VM isn't running
+        # 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 $?