cpus: Introduce cpu_list_generation_id

Introduce cpu_list_generation_id to track cpu list generation so
that cpu hotplug/unplug can be detected during measurement of
dirty page rate.

cpu_list_generation_id could be used to detect changes of cpu
list, which is prepared for dirty page rate measurement.

Signed-off-by: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <06e1f1362b2501a471dce796abb065b04f320fa5.1656177590.git.huangy81@chinatelecom.cn>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

cpus-common.c

@@ -73,6 +73,12 @@ static int cpu_get_free_index(void)
 }
 
 CPUTailQ cpus = QTAILQ_HEAD_INITIALIZER(cpus);
+static unsigned int cpu_list_generation_id;
+
+unsigned int cpu_list_generation_id_get(void)
+{
+    return cpu_list_generation_id;
+}
 
 void cpu_list_add(CPUState *cpu)
 {
@@ -84,6 +90,7 @@ void cpu_list_add(CPUState *cpu)
         assert(!cpu_index_auto_assigned);
     }
     QTAILQ_INSERT_TAIL_RCU(&cpus, cpu, node);
+    cpu_list_generation_id++;
 }
 
 void cpu_list_remove(CPUState *cpu)
@@ -96,6 +103,7 @@ void cpu_list_remove(CPUState *cpu)
 
     QTAILQ_REMOVE_RCU(&cpus, cpu, node);
     cpu->cpu_index = UNASSIGNED_CPU_INDEX;
+    cpu_list_generation_id++;
 }
 
 CPUState *qemu_get_cpu(int index)

include/exec/cpu-common.h

@@ -35,6 +35,7 @@ extern intptr_t qemu_host_page_mask;
 void qemu_init_cpu_list(void);
 void cpu_list_lock(void);
 void cpu_list_unlock(void);
+unsigned int cpu_list_generation_id_get(void);
 
 void tcg_flush_softmmu_tlb(CPUState *cs);