[Qemu-devel] [RFC v3 2/3] scsi: add scsi_bus_dma_restart()

[Stefan Hajnoczi <stefanha@redhat.com>]

By default scsi-bus.c registers vm change state handlers for SCSIDevice
instances and restarts DMA when guest execution is resumed.

Unfortunately virtio-scsi with iothreads has a special ordering
requirement that the core virtio code's vm change state handler runs
before scsi-bus.c's vm change state handler.

This patch allows SCSI busses to disable the default vm change state
handler for DMA restart.  The new scsi_bus_dma_restart() API allows them
to manually restart DMA at a time of their choice.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 include/hw/scsi/scsi.h |  5 +++++
 hw/scsi/scsi-bus.c     | 37 ++++++++++++++++++++++++++++++-------
 2 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/include/hw/scsi/scsi.h b/include/hw/scsi/scsi.h
index acef25faa4..e9cc563daa 100644
--- a/include/hw/scsi/scsi.h
+++ b/include/hw/scsi/scsi.h
@@ -120,6 +120,10 @@ struct SCSIReqOps {
 struct SCSIBusInfo {
     int tcq;
     int max_channel, max_target, max_lun;
+
+    /* Will the bus call scsi_bus_dma_restart() itself? */
+    bool custom_dma_restart;
+
     int (*parse_cdb)(SCSIDevice *dev, SCSICommand *cmd, uint8_t *buf,
                      void *hba_private);
     void (*transfer_data)(SCSIRequest *req, uint32_t arg);
@@ -160,6 +164,7 @@ SCSIDevice *scsi_bus_legacy_add_drive(SCSIBus *bus, BlockBackend *blk,
                                       const char *serial, Error **errp);
 void scsi_bus_legacy_handle_cmdline(SCSIBus *bus);
 void scsi_legacy_handle_cmdline(void);
+void scsi_bus_dma_restart(SCSIBus *bus);
 
 SCSIRequest *scsi_req_alloc(const SCSIReqOps *reqops, SCSIDevice *d,
                             uint32_t tag, uint32_t lun, void *hba_private);
diff --git a/hw/scsi/scsi-bus.c b/hw/scsi/scsi-bus.c
index c480553083..d2c5a1652b 100644
--- a/hw/scsi/scsi-bus.c
+++ b/hw/scsi/scsi-bus.c
@@ -134,6 +134,27 @@ void scsi_req_retry(SCSIRequest *req)
     req->retry = true;
 }
 
+static void scsi_device_dma_restart(SCSIDevice *dev)
+{
+    if (!dev->bh) {
+        AioContext *ctx = blk_get_aio_context(dev->conf.blk);
+        dev->bh = aio_bh_new(ctx, scsi_dma_restart_bh, dev);
+        qemu_bh_schedule(dev->bh);
+    }
+}
+
+void scsi_bus_dma_restart(SCSIBus *bus)
+{
+    BusChild *kid;
+
+    QTAILQ_FOREACH(kid, &bus->qbus.children, sibling) {
+        DeviceState *qdev = kid->child;
+        SCSIDevice *dev = SCSI_DEVICE(qdev);
+
+        scsi_device_dma_restart(dev);
+    }
+}
+
 static void scsi_dma_restart_cb(void *opaque, int running, RunState state)
 {
     SCSIDevice *s = opaque;
@@ -141,11 +162,8 @@ static void scsi_dma_restart_cb(void *opaque, int running, RunState state)
     if (!running) {
         return;
     }
-    if (!s->bh) {
-        AioContext *ctx = blk_get_aio_context(s->conf.blk);
-        s->bh = aio_bh_new(ctx, scsi_dma_restart_bh, s);
-        qemu_bh_schedule(s->bh);
-    }
+
+    scsi_device_dma_restart(s);
 }
 
 static void scsi_qdev_realize(DeviceState *qdev, Error **errp)
@@ -206,8 +224,13 @@ static void scsi_qdev_realize(DeviceState *qdev, Error **errp)
         error_propagate(errp, local_err);
         return;
     }
-    dev->vmsentry = qemu_add_vm_change_state_handler(scsi_dma_restart_cb,
-                                                     dev);
+
+    if (bus->info->custom_dma_restart) {
+        dev->vmsentry = NULL;
+    } else {
+        dev->vmsentry = qemu_add_vm_change_state_handler(scsi_dma_restart_cb,
+                                                         dev);
+    }
 }
 
 static void scsi_qdev_unrealize(DeviceState *qdev, Error **errp)
-- 
2.21.0