[PATCH 2/3] qemu: Introduce job queue size limit

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

This patch creates an optional BeginJob queue size limit. When
active, all other attempts above level will fail. To set this
feature assign desired value to max_queued variable in qemu.conf.
Setting it to 0 turns it off.
---
 src/qemu/libvirtd_qemu.aug |    1 +
 src/qemu/qemu.conf         |    7 +++++++
 src/qemu/qemu_conf.c       |    4 ++++
 src/qemu/qemu_conf.h       |    2 ++
 src/qemu/qemu_domain.c     |   17 +++++++++++++++++
 src/qemu/qemu_domain.h     |    2 ++
 6 files changed, 33 insertions(+), 0 deletions(-)

diff --git a/src/qemu/libvirtd_qemu.aug b/src/qemu/libvirtd_qemu.aug
index d018ac2..6c145c7 100644
--- a/src/qemu/libvirtd_qemu.aug
+++ b/src/qemu/libvirtd_qemu.aug
@@ -51,6 +51,7 @@ module Libvirtd_qemu =
                  | bool_entry "set_process_name"
                  | int_entry "max_processes"
                  | str_entry "lock_manager"
+                 | int_entry "max_queued"
 
    (* Each enty in the config is one of the following three ... *)
    let entry = vnc_entry
diff --git a/src/qemu/qemu.conf b/src/qemu/qemu.conf
index 79c6e85..4da5d5a 100644
--- a/src/qemu/qemu.conf
+++ b/src/qemu/qemu.conf
@@ -309,3 +309,10 @@
 # disk), uncomment this
 #
 # lock_manager = "sanlock"
+
+# Set limit of maximum APIs queued on one domain. All other APIs
+# over this threshold will fail on acquiring job lock. Specially,
+# setting to zero turns this feature off.
+# Note, that job lock is per domain.
+#
+# max_queued = 0
diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
index 443e08d..d1bf075 100644
--- a/src/qemu/qemu_conf.c
+++ b/src/qemu/qemu_conf.c
@@ -458,6 +458,10 @@ int qemudLoadDriverConfig(struct qemud_driver *driver,
         VIR_FREE(lockConf);
     }
 
+    p = virConfGetValue(conf, "max_queued");
+    CHECK_TYPE("max_queued", VIR_CONF_LONG);
+    if (p) driver->max_queued = p->l;
+
     virConfFree (conf);
     return 0;
 }
diff --git a/src/qemu/qemu_conf.h b/src/qemu/qemu_conf.h
index 0a60d32..098e94e 100644
--- a/src/qemu/qemu_conf.h
+++ b/src/qemu/qemu_conf.h
@@ -108,6 +108,8 @@ struct qemud_driver {
 
     int maxProcesses;
 
+    int max_queued;
+
     virCapsPtr caps;
 
     virDomainEventStatePtr domainEventState;
diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 675c6df..982bad6 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -713,6 +713,8 @@ qemuDomainObjBeginJobInternal(struct qemud_driver *driver,
     unsigned long long then;
     bool nested = job == QEMU_JOB_ASYNC_NESTED;
 
+    priv->jobs_queued++;
+
     if (virTimeMs(&now) < 0)
         return -1;
     then = now + QEMU_JOB_WAIT_TIME;
@@ -722,6 +724,11 @@ qemuDomainObjBeginJobInternal(struct qemud_driver *driver,
         qemuDriverUnlock(driver);
 
 retry:
+    if (driver->max_queued &&
+        priv->jobs_queued > driver->max_queued) {
+        goto error;
+    }
+
     while (!nested && !qemuDomainJobAllowed(priv, job)) {
         if (virCondWaitUntil(&priv->job.asyncCond, &obj->lock, then) < 0)
             goto error;
@@ -761,9 +768,15 @@ error:
     if (errno == ETIMEDOUT)
         qemuReportError(VIR_ERR_OPERATION_TIMEOUT,
                         "%s", _("cannot acquire state change lock"));
+    else if (driver->max_queued &&
+             priv->jobs_queued > driver->max_queued)
+        qemuReportError(VIR_ERR_OPERATION_FAILED,
+                        "%s", _("cannot acquire state change lock "
+                                "due to max_queued limit"));
     else
         virReportSystemError(errno,
                              "%s", _("cannot acquire job mutex"));
+    priv->jobs_queued--;
     if (driver_locked) {
         virDomainObjUnlock(obj);
         qemuDriverLock(driver);
@@ -844,6 +857,8 @@ int qemuDomainObjEndJob(struct qemud_driver *driver, virDomainObjPtr obj)
 {
     qemuDomainObjPrivatePtr priv = obj->privateData;
 
+    priv->jobs_queued--;
+
     qemuDomainObjResetJob(priv);
     qemuDomainObjSaveJob(driver, obj);
     virCondSignal(&priv->job.cond);
@@ -856,6 +871,8 @@ qemuDomainObjEndAsyncJob(struct qemud_driver *driver, virDomainObjPtr obj)
 {
     qemuDomainObjPrivatePtr priv = obj->privateData;
 
+    priv->jobs_queued--;
+
     qemuDomainObjResetAsyncJob(priv);
     qemuDomainObjSaveJob(driver, obj);
     virCondBroadcast(&priv->job.asyncCond);
diff --git a/src/qemu/qemu_domain.h b/src/qemu/qemu_domain.h
index e12ca8e..55875fe 100644
--- a/src/qemu/qemu_domain.h
+++ b/src/qemu/qemu_domain.h
@@ -113,6 +113,8 @@ struct _qemuDomainObjPrivate {
     char *lockState;
 
     bool fakeReboot;
+
+    int jobs_queued;
 };
 
 struct qemuDomainWatchdogEvent
-- 
1.7.3.4

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