[Qemu-devel] [PATCH v5 1/3] vl: add qemu_add_vm_change_state_handler_prio()

[Stefan Hajnoczi]

Add an API for registering vm change state handlers with a well-defined
ordering.  This is necessary when handlers depend on each other.

Small coding style fixes are included to make checkpatch.pl happy.

Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
---
 include/sysemu/sysemu.h |  2 ++
 vl.c                    | 59 ++++++++++++++++++++++++++++++++---------
 2 files changed, 49 insertions(+), 12 deletions(-)

diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 61579ae71e..984c439ac9 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -29,6 +29,8 @@ typedef void VMChangeStateHandler(void *opaque, int running, 
RunState state);
 
 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);
 void qemu_del_vm_change_state_handler(VMChangeStateEntry *e);
 void vm_state_notify(int running, RunState state);
 
diff --git a/vl.c b/vl.c
index 99a56b5556..7fac2ae7ca 100644
--- a/vl.c
+++ b/vl.c
@@ -1471,28 +1471,57 @@ static int machine_help_func(QemuOpts *opts, 
MachineState *machine)
 struct vm_change_state_entry {
     VMChangeStateHandler *cb;
     void *opaque;
-    QLIST_ENTRY (vm_change_state_entry) entries;
+    QTAILQ_ENTRY(vm_change_state_entry) entries;
+    int priority;
 };
 
-static QLIST_HEAD(, vm_change_state_entry) vm_change_state_head;
+static QTAILQ_HEAD(, vm_change_state_entry) vm_change_state_head;
 
-VMChangeStateEntry *qemu_add_vm_change_state_handler(VMChangeStateHandler *cb,
-                                                     void *opaque)
+/**
+ * qemu_add_vm_change_state_handler_prio:
+ * @cb: the callback to invoke
+ * @opaque: user data passed to the callback
+ * @priority: low priorities execute first when the vm runs and the reverse is
+ *            true when the vm stops
+ *
+ * Register a callback function that is invoked when the vm starts or stops
+ * running.
+ *
+ * Returns: an entry to be freed using qemu_del_vm_change_state_handler()
+ */
+VMChangeStateEntry *qemu_add_vm_change_state_handler_prio(
+        VMChangeStateHandler *cb, void *opaque, int priority)
 {
     VMChangeStateEntry *e;
+    VMChangeStateEntry *other;
 
-    e = g_malloc0(sizeof (*e));
-
+    e = g_malloc0(sizeof(*e));
     e->cb = cb;
     e->opaque = opaque;
-    QLIST_INSERT_HEAD(&vm_change_state_head, e, entries);
+    e->priority = priority;
+
+    /* Keep list sorted in ascending priority order */
+    QTAILQ_FOREACH(other, &vm_change_state_head, entries) {
+        if (priority < other->priority) {
+            QTAILQ_INSERT_BEFORE(other, e, entries);
+            return e;
+        }
+    }
+
+    QTAILQ_INSERT_TAIL(&vm_change_state_head, e, entries);
     return e;
 }
 
+VMChangeStateEntry *qemu_add_vm_change_state_handler(VMChangeStateHandler *cb,
+                                                     void *opaque)
+{
+    return qemu_add_vm_change_state_handler_prio(cb, opaque, 0);
+}
+
 void qemu_del_vm_change_state_handler(VMChangeStateEntry *e)
 {
-    QLIST_REMOVE (e, entries);
-    g_free (e);
+    QTAILQ_REMOVE(&vm_change_state_head, e, entries);
+    g_free(e);
 }
 
 void vm_state_notify(int running, RunState state)
@@ -1501,8 +1530,14 @@ void vm_state_notify(int running, RunState state)
 
     trace_vm_state_notify(running, state, RunState_str(state));
 
-    QLIST_FOREACH_SAFE(e, &vm_change_state_head, entries, next) {
-        e->cb(e->opaque, running, state);
+    if (running) {
+        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) {
+            e->cb(e->opaque, running, state);
+        }
     }
 }
 
@@ -3025,7 +3060,7 @@ int main(int argc, char **argv, char **envp)
         exit(1);
     }
 
-    QLIST_INIT (&vm_change_state_head);
+    QTAILQ_INIT(&vm_change_state_head);
     os_setup_early_signal_handling();
 
     cpu_option = NULL;
-- 
2.21.0