Re: [libvirt] [PATCH 08/15] Locking of the qemuMonitorPtr object
On Tue, Nov 03, 2009 at 02:50:02PM -0500, Daniel P. Berrange wrote:
In preparation of the monitor I/O process becoming fully
asynchronous,
it is neccessary to ensure all access to internals of the qemuMonitorPtr
object is protected by a mutex lock.
* src/qemu/qemu_monitor.c, src/qemu/qemu_monitor.h: Add mutex for locking
monitor.
* src/qemu/qemu_driver.c: Add locking around all monitor commands
---
src/qemu/qemu_driver.c | 299 +++++++++++++++++++++++++++++++++++------------
src/qemu/qemu_monitor.c | 19 +++
src/qemu/qemu_monitor.h | 3 +
3 files changed, 248 insertions(+), 73 deletions(-)
[..]
+++ b/src/qemu/qemu_driver.c
@@ -141,6 +141,22 @@ static void qemuDomainObjPrivateFree(void *data)
}
+static void qemuDomainObjEnterMonitor(virDomainObjPtr obj)
+{
+ qemuDomainObjPrivatePtr priv = obj->privateData;
+
+ qemuMonitorLock(priv->mon);
+}
+
+
+static void qemuDomainObjExitMonitor(virDomainObjPtr obj)
+{
+ qemuDomainObjPrivatePtr priv = obj->privateData;
+
+ qemuMonitorUnlock(priv->mon);
+}
+
so we're using pthread mutex here and basically there is no way this
could go wrong and there is no need to handle errors, okay
static int qemuCgroupControllerActive(struct qemud_driver *driver,
int controller)
{
the patch is quite regular
+ qemuDomainObjEnterMonitor(vm);
+ if (qemuMonitorStopCPUs(priv->mon) < 0) {
+ qemuDomainObjExitMonitor(vm);
goto cleanup;
+ }
+ qemuDomainObjExitMonitor(vm);
to some extend I wonder if we shouldn't kill all those blocks and
always use the more regular form
qemuDomainObjEnterMonitor(vm);
ret = qemuMonitorStopCPUs(priv->mon);
qemuDomainObjExitMonitor(vm);
if (ret < 0)
goto cleanup;
it's simpler, easier to read, we don't have to think about matching
of Enter and Exit, and the generated code probably will be identical
In a number of places the refactoring introduced the later way but
the former is still present in a number of place, closer to original
code but doesn't make the patch safer I'm afraid. The only inconvenience
is the declaration of the temporary variable ...
[...]
+void qemuMonitorLock(qemuMonitorPtr mon)
+{
+ virMutexLock(&mon->lock);
+}
+
+void qemuMonitorUnlock(qemuMonitorPtr mon)
+{
+ virMutexUnlock(&mon->lock);
+}
okay no error possible ...
Okay, I didn't spot anything suspect in the locking patch. But as
usual the problems may be in parts we may have forgotten about. Also
sometime the patch shows only a fraction of the relevant code.
Best is to push and test, ACK !
Daniel
--
Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/
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