scsi: Introduce scsi_req_cancel_async

Devices will call this function to start an asynchronous cancellation. The
bus->info->cancel will be called after the request is canceled.

Devices will probably need to track a separate TMF request that triggers this
cancellation, and wait until the cancellation is done before completing it. So
we store a notifier list in SCSIRequest and in scsi_req_cancel_complete we
notify them.

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/scsi/scsi-bus.c

@@ -566,6 +566,7 @@ SCSIRequest *scsi_req_alloc(const SCSIReqOps *reqops, SCSIDevice *d,
     req->ops = reqops;
     object_ref(OBJECT(d));
     object_ref(OBJECT(qbus->parent));
+    notifier_list_init(&req->cancel_notifiers);
     trace_scsi_req_alloc(req->dev->id, req->lun, req->tag);
     return req;
 }
@@ -1715,6 +1716,9 @@ void scsi_req_complete(SCSIRequest *req, int status)
     scsi_req_ref(req);
     scsi_req_dequeue(req);
     req->bus->info->complete(req, req->status, req->resid);
+
+    /* Cancelled requests might end up being completed instead of cancelled */
+    notifier_list_notify(&req->cancel_notifiers, req);
     scsi_req_unref(req);
 }
 
@@ -1725,9 +1729,31 @@ void scsi_req_cancel_complete(SCSIRequest *req)
     if (req->bus->info->cancel) {
         req->bus->info->cancel(req);
     }
+    notifier_list_notify(&req->cancel_notifiers, req);
     scsi_req_unref(req);
 }
 
+/* Cancel @req asynchronously. @notifier is added to @req's cancellation
+ * notifier list, the bus will be notified the requests cancellation is
+ * completed.
+ * */
+void scsi_req_cancel_async(SCSIRequest *req, Notifier *notifier)
+{
+    trace_scsi_req_cancel(req->dev->id, req->lun, req->tag);
+    if (notifier) {
+        notifier_list_add(&req->cancel_notifiers, notifier);
+    }
+    if (req->io_canceled) {
+        return;
+    }
+    scsi_req_ref(req);
+    scsi_req_dequeue(req);
+    req->io_canceled = true;
+    if (req->aiocb) {
+        bdrv_aio_cancel_async(req->aiocb);
+    }
+}
+
 void scsi_req_cancel(SCSIRequest *req)
 {
     trace_scsi_req_cancel(req->dev->id, req->lun, req->tag);

include/hw/scsi/scsi.h

@@ -5,6 +5,7 @@
 #include "block/block.h"
 #include "hw/block/block.h"
 #include "sysemu/sysemu.h"
+#include "qemu/notify.h"
 
 #define MAX_SCSI_DEVS	255
 
@@ -53,6 +54,7 @@ struct SCSIRequest {
     void              *hba_private;
     size_t            resid;
     SCSICommand       cmd;
+    NotifierList      cancel_notifiers;
 
     /* Note:
      * - fields before sense are initialized by scsi_req_alloc;
@@ -266,6 +268,7 @@ uint8_t *scsi_req_get_buf(SCSIRequest *req);
 int scsi_req_get_sense(SCSIRequest *req, uint8_t *buf, int len);
 void scsi_req_cancel_complete(SCSIRequest *req);
 void scsi_req_cancel(SCSIRequest *req);
+void scsi_req_cancel_async(SCSIRequest *req, Notifier *notifier);
 void scsi_req_retry(SCSIRequest *req);
 void scsi_device_purge_requests(SCSIDevice *sdev, SCSISense sense);
 void scsi_device_set_ua(SCSIDevice *sdev, SCSISense sense);