[RFC PATCH 2/7] cpus: Introduce AccelOpsClass::get_cpus_queue()

[Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>]

We want the ability to iterate over vCPUs of a specific
accelerator.  Introduce cpus_get_accel_cpus_queue() to
be used by accelerator common code, and expose the
get_cpus_queue() in AccelOpsClass, so each accelerator
can register its own queue of vCPUs.

Signed-off-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
---
 include/hw/core/cpu.h      |  8 ++++++++
 include/system/accel-ops.h |  6 ++++++
 accel/tcg/user-exec-stub.c |  5 +++++
 cpu-common.c               | 10 ++++++++++
 system/cpus.c              |  5 +++++
 5 files changed, 34 insertions(+)

diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
index 48d90f50a71..5ae9bb64d6e 100644
--- a/include/hw/core/cpu.h
+++ b/include/hw/core/cpu.h
@@ -591,6 +591,14 @@ static inline CPUArchState *cpu_env(CPUState *cpu)
 typedef QTAILQ_HEAD(CPUTailQ, CPUState) CPUTailQ;
 extern CPUTailQ cpus_queue;
 
+/**
+ * cpus_get_accel_cpus_queue:
+ * @cpu: The vCPU to get the accelerator #CPUTailQ.
+ *
+ * Returns the #CPUTailQ associated with the accelerator of the vCPU.
+ */
+CPUTailQ *cpus_get_accel_cpus_queue(CPUState *cpu);
+
 #define first_cpu        QTAILQ_FIRST_RCU(&cpus_queue)
 #define CPU_NEXT(cpu)    QTAILQ_NEXT_RCU(cpu, node)
 #define CPU_FOREACH(cpu) QTAILQ_FOREACH_RCU(cpu, &cpus_queue, node)
diff --git a/include/system/accel-ops.h b/include/system/accel-ops.h
index 137fb96d444..fe59f728bfc 100644
--- a/include/system/accel-ops.h
+++ b/include/system/accel-ops.h
@@ -12,6 +12,7 @@
 
 #include "exec/vaddr.h"
 #include "qom/object.h"
+#include "hw/core/cpu.h"
 
 #define ACCEL_OPS_SUFFIX "-ops"
 #define TYPE_ACCEL_OPS "accel" ACCEL_OPS_SUFFIX
@@ -37,6 +38,11 @@ struct AccelOpsClass {
     bool (*cpus_are_resettable)(void);
     void (*cpu_reset_hold)(CPUState *cpu);
 
+    /**
+     * get_cpus_queue:
+     * Returns the #CPUTailQ maintained by this accelerator.
+     */
+    CPUTailQ *(*get_cpus_queue)(void);
     void (*create_vcpu_thread)(CPUState *cpu); /* MANDATORY NON-NULL */
     void (*kick_vcpu_thread)(CPUState *cpu);
     bool (*cpu_thread_is_idle)(CPUState *cpu);
diff --git a/accel/tcg/user-exec-stub.c b/accel/tcg/user-exec-stub.c
index 4fbe2dbdc88..cb76cec76be 100644
--- a/accel/tcg/user-exec-stub.c
+++ b/accel/tcg/user-exec-stub.c
@@ -18,6 +18,11 @@ void cpu_exec_reset_hold(CPUState *cpu)
 {
 }
 
+CPUTailQ *cpus_get_accel_cpus_queue(CPUState *cpu)
+{
+    return NULL;
+}
+
 /* User mode emulation does not support record/replay yet.  */
 
 bool replay_exception(void)
diff --git a/cpu-common.c b/cpu-common.c
index 4248b2d727e..ff8db9c7f9d 100644
--- a/cpu-common.c
+++ b/cpu-common.c
@@ -82,6 +82,7 @@ unsigned int cpu_list_generation_id_get(void)
 void cpu_list_add(CPUState *cpu)
 {
     static bool cpu_index_auto_assigned;
+    CPUTailQ *accel_cpus_queue = cpus_get_accel_cpus_queue(cpu);
 
     QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
     if (cpu->cpu_index == UNASSIGNED_CPU_INDEX) {
@@ -92,17 +93,26 @@ void cpu_list_add(CPUState *cpu)
         assert(!cpu_index_auto_assigned);
     }
     QTAILQ_INSERT_TAIL_RCU(&cpus_queue, cpu, node);
+    if (accel_cpus_queue) {
+        QTAILQ_INSERT_TAIL_RCU(accel_cpus_queue, cpu, node);
+    }
+
     cpu_list_generation_id++;
 }
 
 void cpu_list_remove(CPUState *cpu)
 {
+    CPUTailQ *accel_cpus_queue = cpus_get_accel_cpus_queue(cpu);
+
     QEMU_LOCK_GUARD(&qemu_cpu_list_lock);
     if (!QTAILQ_IN_USE(cpu, node)) {
         /* there is nothing to undo since cpu_exec_init() hasn't been called */
         return;
     }
 
+    if (accel_cpus_queue) {
+        QTAILQ_REMOVE_RCU(accel_cpus_queue, cpu, node);
+    }
     QTAILQ_REMOVE_RCU(&cpus_queue, cpu, node);
     cpu->cpu_index = UNASSIGNED_CPU_INDEX;
     cpu_list_generation_id++;
diff --git a/system/cpus.c b/system/cpus.c
index 99f83806c16..972df6ab061 100644
--- a/system/cpus.c
+++ b/system/cpus.c
@@ -209,6 +209,11 @@ void cpu_exec_reset_hold(CPUState *cpu)
     }
 }
 
+CPUTailQ *cpus_get_accel_cpus_queue(CPUState *cpu)
+{
+    return cpus_accel ? cpus_accel->get_cpus_queue() : NULL;
+}
+
 int64_t cpus_get_virtual_clock(void)
 {
     /*
-- 
2.47.1