libxl: Add lock process indicator to libxlDomainObjPrivate object

The libvirt libxl driver has no access to FDs associated with VM disks.
The disks are opened by libxl.so and any related FDs are not exposed to
applications. The prevents using virtlockd's auto-release feature to
release locks when the FD is closed. Acquiring and releasing locks is
explicitly handled by the libxl driver.

The current logic is structured such that locks are acquired in
libxlDomainStart and released in libxlDomainCleanup. This works well
except for migration, where the locks must be released on the source
host before the domain can be started on the destination host, but the
domain cannot be cleaned up until the migration confirmation stage.
When libxlDomainCleanup if finally called in the confirm stage, locks
are again released resulting in confusing errors from virtlockd and
libvirtd

virtlockd[8095]: resource busy: Lockspace resource 'xxxxxx' is not locked
libvirtd[8050]: resource busy: Lockspace resource 'xxxxxx' is not locked
libvirtd[8050]: Unable to release lease on testvm

The error is also encountered in some error cases, e.g. when
libxlDomainStart fails before acquiring locks and libxlDomainCleanup
is still used for cleanup.

In lieu of a mechanism to check if a lock has been acquired, this patch
takes an easy approach to fixing the unnecessary lock releases by adding
an indicator to the libxlDomainPrivate object that can be set when the
lock is acquired and cleared when the lock is released. libxlDomainCleanup
can then skip releasing the lock in cases where it was previously released
or never acquired in the first place.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

diff --git a/src/libxl/libxl_domain.c b/src/libxl/libxl_domain.c
index 604b94a00685518549e53226a370bc3e08ca1a60..014f6aceca024763c26861abfcb76f5149488f48 100644 (file)
--- a/src/libxl/libxl_domain.c
+++ b/src/libxl/libxl_domain.c
@@ -861,10 +861,14 @@ libxlDomainCleanup(libxlDriverPrivatePtr driver,
     virHostdevReAttachDomainDevices(hostdev_mgr, LIBXL_DRIVER_INTERNAL_NAME,
                                     vm->def, hostdev_flags);
 
-    VIR_FREE(priv->lockState);
-    if (virDomainLockProcessPause(driver->lockManager, vm, &priv->lockState) < 0)
-        VIR_WARN("Unable to release lease on %s", vm->def->name);
-    VIR_DEBUG("Preserving lock state '%s'", NULLSTR(priv->lockState));
+    if (priv->lockProcessRunning) {
+        VIR_FREE(priv->lockState);
+        if (virDomainLockProcessPause(driver->lockManager, vm, &priv->lockState) < 0)
+            VIR_WARN("Unable to release lease on %s", vm->def->name);
+        else
+            priv->lockProcessRunning = false;
+        VIR_DEBUG("Preserving lock state '%s'", NULLSTR(priv->lockState));
+    }
 
     libxlLoggerCloseFile(cfg->logger, vm->def->id);
     vm->def->id = -1;
@@ -1426,6 +1430,7 @@ libxlDomainStart(libxlDriverPrivatePtr driver,
                                   priv->lockState) < 0)
         goto destroy_dom;
     VIR_FREE(priv->lockState);
+    priv->lockProcessRunning = true;
 
     /* Always enable domain death events */
     if (libxl_evenable_domain_death(cfg->ctx, vm->def->id, 0, &priv->deathW))

diff --git a/src/libxl/libxl_domain.h b/src/libxl/libxl_domain.h
index 00682546e01060abfc16cbebe9a56240212cfae0..5fb76bd303b7a075b3fae1be03df20d903874862 100644 (file)
--- a/src/libxl/libxl_domain.h
+++ b/src/libxl/libxl_domain.h
@@ -68,6 +68,7 @@ struct _libxlDomainObjPrivate {
     virThreadPtr migrationDstReceiveThr;
     unsigned short migrationPort;
     char *lockState;
+    bool lockProcessRunning;
 
     struct libxlDomainJobObj job;
 

diff --git a/src/libxl/libxl_migration.c b/src/libxl/libxl_migration.c
index 631f67930dc6c7e8bf60a289b4e94f446c260266..a5a9df98ad7c48b1117207a18f052ac12a4bea68 100644 (file)
--- a/src/libxl/libxl_migration.c
+++ b/src/libxl/libxl_migration.c
@@ -1242,9 +1242,12 @@ libxlDomainMigrationSrcPerform(libxlDriverPrivatePtr driver,
     virObjectLock(vm);
 
     if (ret == 0) {
-        if (virDomainLockProcessPause(driver->lockManager, vm, &priv->lockState) < 0)
+        if (virDomainLockProcessPause(driver->lockManager, vm, &priv->lockState) == 0) {
+            priv->lockProcessRunning = false;
+            VIR_DEBUG("Preserving lock state '%s'", NULLSTR(priv->lockState));
+        } else {
             VIR_WARN("Unable to release lease on %s", vm->def->name);
-        VIR_DEBUG("Preserving lock state '%s'", NULLSTR(priv->lockState));
+        }
     } else {
         /*
          * Confirm phase will not be executed if perform fails. End the
@@ -1377,6 +1380,7 @@ libxlDomainMigrationSrcConfirm(libxlDriverPrivatePtr driver,
                                    "xen:///system",
                                    vm,
                                    priv->lockState);
+        priv->lockProcessRunning = true;
         if (libxl_domain_resume(cfg->ctx, vm->def->id, 1, 0) == 0) {
             ret = 0;
         } else {