util/vhost-user-server: rename refcount to in_flight counter

The VuServer object has a refcount field and ref/unref APIs. The name is
confusing because it's actually an in-flight request counter instead of
a refcount.

Normally a refcount destroys the object upon reaching zero. The VuServer
counter is used to wake up the vhost-user coroutine when there are no
more requests.

Avoid confusing by renaming refcount and ref/unref to in_flight and
inc/dec.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230516190238.8401-6-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/export/vhost-user-blk-server.c

@@ -50,7 +50,10 @@ static void vu_blk_req_complete(VuBlkReq *req, size_t in_len)
     free(req);
 }
 
-/* Called with server refcount increased, must decrease before returning */
+/*
+ * Called with server in_flight counter increased, must decrease before
+ * returning.
+ */
 static void coroutine_fn vu_blk_virtio_process_req(void *opaque)
 {
     VuBlkReq *req = opaque;
@@ -68,12 +71,12 @@ static void coroutine_fn vu_blk_virtio_process_req(void *opaque)
                                     in_num, out_num);
     if (in_len < 0) {
         free(req);
-        vhost_user_server_unref(server);
+        vhost_user_server_dec_in_flight(server);
         return;
     }
 
     vu_blk_req_complete(req, in_len);
-    vhost_user_server_unref(server);
+    vhost_user_server_dec_in_flight(server);
 }
 
 static void vu_blk_process_vq(VuDev *vu_dev, int idx)
@@ -95,7 +98,7 @@ static void vu_blk_process_vq(VuDev *vu_dev, int idx)
         Coroutine *co =
             qemu_coroutine_create(vu_blk_virtio_process_req, req);
 
-        vhost_user_server_ref(server);
+        vhost_user_server_inc_in_flight(server);
         qemu_coroutine_enter(co);
     }
 }

include/qemu/vhost-user-server.h

@@ -41,7 +41,7 @@ typedef struct {
     const VuDevIface *vu_iface;
 
     /* Protected by ctx lock */
-    unsigned int refcount;
+    unsigned int in_flight;
     bool wait_idle;
     VuDev vu_dev;
     QIOChannel *ioc; /* The I/O channel with the client */
@@ -60,8 +60,8 @@ bool vhost_user_server_start(VuServer *server,
 
 void vhost_user_server_stop(VuServer *server);
 
-void vhost_user_server_ref(VuServer *server);
-void vhost_user_server_unref(VuServer *server);
+void vhost_user_server_inc_in_flight(VuServer *server);
+void vhost_user_server_dec_in_flight(VuServer *server);
 
 void vhost_user_server_attach_aio_context(VuServer *server, AioContext *ctx);
 void vhost_user_server_detach_aio_context(VuServer *server);

util/vhost-user-server.c

@@ -75,16 +75,16 @@ static void panic_cb(VuDev *vu_dev, const char *buf)
     error_report("vu_panic: %s", buf);
 }
 
-void vhost_user_server_ref(VuServer *server)
+void vhost_user_server_inc_in_flight(VuServer *server)
 {
     assert(!server->wait_idle);
-    server->refcount++;
+    server->in_flight++;
 }
 
-void vhost_user_server_unref(VuServer *server)
+void vhost_user_server_dec_in_flight(VuServer *server)
 {
-    server->refcount--;
-    if (server->wait_idle && !server->refcount) {
+    server->in_flight--;
+    if (server->wait_idle && !server->in_flight) {
         aio_co_wake(server->co_trip);
     }
 }
@@ -192,13 +192,13 @@ static coroutine_fn void vu_client_trip(void *opaque)
         /* Keep running */
     }
 
-    if (server->refcount) {
+    if (server->in_flight) {
         /* Wait for requests to complete before we can unmap the memory */
         server->wait_idle = true;
         qemu_coroutine_yield();
         server->wait_idle = false;
     }
-    assert(server->refcount == 0);
+    assert(server->in_flight == 0);
 
     vu_deinit(vu_dev);