Re: [PATCH for-8.2 2/6] sysemu: Add pre VM state change callback

[Cédric Le Goater]

On 7/16/23 10:15, Avihai Horon wrote:

Add pre VM state change callback to struct VMChangeStateEntry.

This sentence could be the subject.

The pre VM state change callback is optional and can be set by the new
function qemu_add_vm_change_state_handler_prio_full() that allows
setting this callback in addition to the main callback.

The pre VM state change callbacks and main callbacks are called in two
separate phases: First all pre VM state change callbacks are called and
only then all main callbacks are called.

The purpose of the new pre VM state change callback is to allow all
devices to run a preliminary task before calling the devices' main
callbacks.

This will facilitate adding P2P support for VFIO migration where all
VFIO devices need to be put in an intermediate P2P quiescent state
before being stopped or started by the main VM state change callback.

Signed-off-by: Avihai Horon <avih...@nvidia.com>
---
  include/sysemu/runstate.h |  4 ++++
  softmmu/runstate.c        | 39 +++++++++++++++++++++++++++++++++++++++
  2 files changed, 43 insertions(+)

diff --git a/include/sysemu/runstate.h b/include/sysemu/runstate.h
index 7beb29c2e2..bb38a4b4bd 100644
--- a/include/sysemu/runstate.h
+++ b/include/sysemu/runstate.h
@@ -16,6 +16,10 @@ VMChangeStateEntry 
*qemu_add_vm_change_state_handler(VMChangeStateHandler *cb,
                                                       void *opaque);
  VMChangeStateEntry *qemu_add_vm_change_state_handler_prio(
          VMChangeStateHandler *cb, void *opaque, int priority);
+VMChangeStateEntry *
+qemu_add_vm_change_state_handler_prio_full(VMChangeStateHandler *cb,
+                                           VMChangeStateHandler *pre_change_cb,
+                                           void *opaque, int priority);
  VMChangeStateEntry *qdev_add_vm_change_state_handler(DeviceState *dev,
                                                       VMChangeStateHandler *cb,
                                                       void *opaque);
diff --git a/softmmu/runstate.c b/softmmu/runstate.c
index f3bd862818..a1f0653899 100644
--- a/softmmu/runstate.c
+++ b/softmmu/runstate.c
@@ -271,6 +271,7 @@ void qemu_system_vmstop_request(RunState state)
  }
  struct VMChangeStateEntry {
      VMChangeStateHandler *cb;
+    VMChangeStateHandler *pre_change_cb;

I propose to use 'prepare' instead of 'pre_change'

      void *opaque;
      QTAILQ_ENTRY(VMChangeStateEntry) entries;
      int priority;
@@ -293,12 +294,38 @@ static QTAILQ_HEAD(, VMChangeStateEntry) 
vm_change_state_head =
   */
  VMChangeStateEntry *qemu_add_vm_change_state_handler_prio(
          VMChangeStateHandler *cb, void *opaque, int priority)
+{
+    return qemu_add_vm_change_state_handler_prio_full(cb, NULL, opaque,
+                                                      priority);
+}
+
+/**
+ * qemu_add_vm_change_state_handler_prio_full:

qemu_add_vm_change_state_handler_prio_all() may be. I don't have much better
but 'full' doesn't sound right. minor.

The rest looks fine to me.

Thanks,

C.

+ * @cb: the main callback to invoke
+ * @pre_change_cb: a callback to invoke before the main callback
+ * @opaque: user data passed to the callbacks
+ * @priority: low priorities execute first when the vm runs and the reverse is
+ *            true when the vm stops
+ *
+ * Register a main callback function and an optional pre VM state change
+ * callback function that are invoked when the vm starts or stops running. The
+ * main callback and the pre VM state change callback are called in two
+ * separate phases: First all pre VM state change callbacks are called and only
+ * then all main callbacks are called.
+ *
+ * Returns: an entry to be freed using qemu_del_vm_change_state_handler()
+ */
+VMChangeStateEntry *
+qemu_add_vm_change_state_handler_prio_full(VMChangeStateHandler *cb,
+                                           VMChangeStateHandler *pre_change_cb,
+                                           void *opaque, int priority)
  {
      VMChangeStateEntry *e;
      VMChangeStateEntry *other;

e = g_malloc0(sizeof(*e));

      e->cb = cb;
+    e->pre_change_cb = pre_change_cb;
      e->opaque = opaque;
      e->priority = priority;

@@ -333,10 +360,22 @@ void vm_state_notify(bool running, RunState state)

      trace_vm_state_notify(running, state, RunState_str(state));

if (running) {

+        QTAILQ_FOREACH_SAFE(e, &vm_change_state_head, entries, next) {
+            if (e->pre_change_cb) {
+                e->pre_change_cb(e->opaque, running, state);
+            }
+        }
+
          QTAILQ_FOREACH_SAFE(e, &vm_change_state_head, entries, next) {
              e->cb(e->opaque, running, state);
          }
      } else {
+        QTAILQ_FOREACH_REVERSE_SAFE(e, &vm_change_state_head, entries, next) {
+            if (e->pre_change_cb) {
+                e->pre_change_cb(e->opaque, running, state);
+            }
+        }
+
          QTAILQ_FOREACH_REVERSE_SAFE(e, &vm_change_state_head, entries, next) {
              e->cb(e->opaque, running, state);
          }