[libvirt] [PATCH] qemu: Prevent disk corruption on domain shutdown

[Jiri Denemark]

Ever since we introduced fake reboot, we call qemuProcessKill as a
reaction to SHUTDOWN event. Unfortunately, qemu doesn't guarantee it
flushed all internal buffers before sending SHUTDOWN, in which case
killing the process forcibly may result in (virtual) disk corruption.

By sending SIGQUIT instead of SIGTERM followed by SIGKILL we tell qemu
to flush all buffers and exit. Once qemu exits, we will see an EOF on
monitor connection and tear down the domain. In case qemu ignores
SIGQUIT or just hangs there, the process stays running but that's not
any different from a possible hang anytime during the shutdown process
so I think it's just fine.
---
 src/qemu/qemu_process.c |   21 +++++++++++++++++++--
 src/qemu/qemu_process.h |    1 +
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index f8a8475..8a12e2a 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -445,12 +445,12 @@ qemuProcessHandleShutdown(qemuMonitorPtr mon ATTRIBUTE_UNUSED,
                             qemuProcessFakeReboot,
                             vm) < 0) {
             VIR_ERROR(_("Failed to create reboot thread, killing domain"));
-            qemuProcessKill(vm);
+            qemuProcessQuit(vm);
             if (virDomainObjUnref(vm) == 0)
                 vm = NULL;
         }
     } else {
-        qemuProcessKill(vm);
+        qemuProcessQuit(vm);
     }
     if (vm)
         virDomainObjUnlock(vm);
@@ -3182,6 +3182,23 @@ cleanup:
 }
 
 
+void qemuProcessQuit(virDomainObjPtr vm)
+{
+    VIR_DEBUG("vm=%s pid=%d", vm->def->name, vm->pid);
+
+    if (!virDomainObjIsActive(vm)) {
+        VIR_DEBUG("VM '%s' not active", vm->def->name);
+        return;
+    }
+
+    if (virKillProcess(vm->pid, SIGQUIT) < 0 && errno != ESRCH) {
+        char ebuf[1024];
+        VIR_WARN("Failed to kill process %d: %s",
+                 vm->pid, virStrerror(errno, ebuf, sizeof(ebuf)));
+    }
+}
+
+
 void qemuProcessKill(virDomainObjPtr vm)
 {
     int i;
diff --git a/src/qemu/qemu_process.h b/src/qemu/qemu_process.h
index 96ba3f3..ad14cf7 100644
--- a/src/qemu/qemu_process.h
+++ b/src/qemu/qemu_process.h
@@ -68,6 +68,7 @@ int qemuProcessAttach(virConnectPtr conn,
                       virDomainChrSourceDefPtr monConfig,
                       bool monJSON);
 
+void qemuProcessQuit(virDomainObjPtr vm);
 void qemuProcessKill(virDomainObjPtr vm);
 
 int qemuProcessAutoDestroyInit(struct qemud_driver *driver);
-- 
1.7.6.1