[PATCH v4 8/8] qemu: Enable for vCPUs on hotplug

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

As advertised in the previous commit, QEMU_SCHED_CORE_VCPUS case
is implemented for hotplug case. The implementation is very
similar to the cold boot case, except here we fork off for every
vCPU (because the implementation is done in
qemuProcessSetupVcpu() which is also the function that's called
from hotplug code). But that's okay because our hotplug APIs
allow hotplugging one device at the time.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2074559
Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---
 src/qemu/qemu_hotplug.c |  2 +-
 src/qemu/qemu_process.c | 61 +++++++++++++++++++++++++++++++++++++++--
 src/qemu/qemu_process.h |  3 +-
 3 files changed, 62 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
index 751fa84013..5f3430d2ba 100644
--- a/src/qemu/qemu_hotplug.c
+++ b/src/qemu/qemu_hotplug.c
@@ -6243,7 +6243,7 @@ qemuDomainHotplugAddVcpu(virQEMUDriver *driver,
         vcpuinfo->online = true;
 
         if (vcpupriv->tid > 0 &&
-            qemuProcessSetupVcpu(vm, i) < 0)
+            qemuProcessSetupVcpu(vm, i, true) < 0)
             return -1;
     }
 
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 83fcb5518a..6e454beb5c 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -5818,10 +5818,40 @@ qemuProcessNetworkPrepareDevices(virQEMUDriver *driver,
 }
 
 
+struct qemuProcessSetupVcpuSchedCoreHelperData {
+    pid_t vcpupid;
+    pid_t dummypid;
+};
+
+static int
+qemuProcessSetupVcpuSchedCoreHelper(pid_t ppid G_GNUC_UNUSED,
+                                    void *opaque)
+{
+    struct qemuProcessSetupVcpuSchedCoreHelperData *data = opaque;
+
+    if (virProcessSchedCoreShareFrom(data->dummypid) < 0) {
+        virReportSystemError(errno,
+                             _("unable to share scheduling cookie from %lld"),
+                             (long long) data->dummypid);
+        return -1;
+    }
+
+    if (virProcessSchedCoreShareTo(data->vcpupid) < 0) {
+        virReportSystemError(errno,
+                             _("unable to share scheduling cookie to %lld"),
+                             (long long) data->vcpupid);
+        return -1;
+    }
+
+    return 0;
+}
+
+
 /**
  * qemuProcessSetupVcpu:
  * @vm: domain object
  * @vcpuid: id of VCPU to set defaults
+ * @schedCore: whether to set scheduling group
  *
  * This function sets resource properties (cgroups, affinity, scheduler) for a
  * vCPU. This function expects that the vCPU is online and the vCPU pids were
@@ -5831,8 +5861,11 @@ qemuProcessNetworkPrepareDevices(virQEMUDriver *driver,
  */
 int
 qemuProcessSetupVcpu(virDomainObj *vm,
-                     unsigned int vcpuid)
+                     unsigned int vcpuid,
+                     bool schedCore)
 {
+    qemuDomainObjPrivate *priv = vm->privateData;
+    g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(priv->driver);
     pid_t vcpupid = qemuDomainGetVcpuPid(vm, vcpuid);
     virDomainVcpuDef *vcpu = virDomainDefGetVcpu(vm->def, vcpuid);
     virDomainResctrlMonDef *mon = NULL;
@@ -5845,6 +5878,30 @@ qemuProcessSetupVcpu(virDomainObj *vm,
                             &vcpu->sched) < 0)
         return -1;
 
+    if (schedCore &&
+        cfg->schedCore == QEMU_SCHED_CORE_VCPUS) {
+        struct qemuProcessSetupVcpuSchedCoreHelperData data = { .vcpupid = vcpupid,
+            .dummypid = -1 };
+
+        for (i = 0; i < virDomainDefGetVcpusMax(vm->def); i++) {
+            pid_t temptid = qemuDomainGetVcpuPid(vm, i);
+
+            if (temptid > 0) {
+                data.dummypid = temptid;
+                break;
+            }
+        }
+
+        if (data.dummypid == -1) {
+            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                           _("Unable to find a vCPU that is online"));
+            return -1;
+        }
+
+        if (virProcessRunInFork(qemuProcessSetupVcpuSchedCoreHelper, &data) < 0)
+            return -1;
+    }
+
     for (i = 0; i < vm->def->nresctrls; i++) {
         size_t j = 0;
         virDomainResctrlDef *ct = vm->def->resctrls[i];
@@ -5951,7 +6008,7 @@ qemuProcessSetupVcpus(virDomainObj *vm)
         if (!vcpu->online)
             continue;
 
-        if (qemuProcessSetupVcpu(vm, i) < 0)
+        if (qemuProcessSetupVcpu(vm, i, false) < 0)
             return -1;
     }
 
diff --git a/src/qemu/qemu_process.h b/src/qemu/qemu_process.h
index 421efc6016..4dfb2485c0 100644
--- a/src/qemu/qemu_process.h
+++ b/src/qemu/qemu_process.h
@@ -187,7 +187,8 @@ int qemuConnectAgent(virQEMUDriver *driver, virDomainObj *vm);
 
 
 int qemuProcessSetupVcpu(virDomainObj *vm,
-                         unsigned int vcpuid);
+                         unsigned int vcpuid,
+                         bool schedCore);
 int qemuProcessSetupIOThread(virDomainObj *vm,
                              virDomainIOThreadIDDef *iothread);
 
-- 
2.35.1