[Qemu-devel] [PATCH master/0.14 2/2] virtio-serial: Add older machine compat property for flow control

[Amit Shah]

Add a compat property for older machine types.  When this is used (via
-M pc-0.13, for example), the new flow control mechanisms will not be
used.  This is done to keep migration from a machine started with older
type on a pc-0.14+ qemu to an older machine working.

The property is named 'flow_control' and defaults to on.

Reported-by: Alex Williamson <address@hidden>
Signed-off-by: Amit Shah <address@hidden>
---
 hw/pc_piix.c           |   16 ++++++++++
 hw/virtio-pci.c        |    2 +
 hw/virtio-serial-bus.c |   77 +++++++++++++++++++++++++++++++++++++++++-------
 hw/virtio-serial.h     |   12 +++++++
 4 files changed, 96 insertions(+), 11 deletions(-)

diff --git a/hw/pc_piix.c b/hw/pc_piix.c
index 7b74473..05b0449 100644
--- a/hw/pc_piix.c
+++ b/hw/pc_piix.c
@@ -243,6 +243,10 @@ static QEMUMachine pc_machine_v0_13 = {
             .driver   = "PCI",
             .property = "command_serr_enable",
             .value    = "off",
+        },{
+            .driver   = "virtio-serial-pci",
+            .property = "flow_control",
+            .value    = stringify(0),
         },
         { /* end of list */ }
     },
@@ -263,6 +267,10 @@ static QEMUMachine pc_machine_v0_12 = {
             .property = "vectors",
             .value    = stringify(0),
         },{
+            .driver   = "virtio-serial-pci",
+            .property = "flow_control",
+            .value    = stringify(0),
+        },{
             .driver   = "VGA",
             .property = "rombar",
             .value    = stringify(0),
@@ -298,6 +306,10 @@ static QEMUMachine pc_machine_v0_11 = {
             .property = "vectors",
             .value    = stringify(0),
         },{
+            .driver   = "virtio-serial-pci",
+            .property = "flow_control",
+            .value    = stringify(0),
+        },{
             .driver   = "ide-drive",
             .property = "ver",
             .value    = "0.11",
@@ -341,6 +353,10 @@ static QEMUMachine pc_machine_v0_10 = {
             .property = "vectors",
             .value    = stringify(0),
         },{
+            .driver   = "virtio-serial-pci",
+            .property = "flow_control",
+            .value    = stringify(0),
+        },{
             .driver   = "virtio-net-pci",
             .property = "vectors",
             .value    = stringify(0),
diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index 952b5d2..530ce9d 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -904,6 +904,8 @@ static PCIDeviceInfo virtio_info[] = {
             DEFINE_VIRTIO_COMMON_FEATURES(VirtIOPCIProxy, host_features),
             DEFINE_PROP_UINT32("max_ports", VirtIOPCIProxy,
                                serial.max_virtserial_ports, 31),
+            DEFINE_PROP_UINT32("flow_control", VirtIOPCIProxy,
+                               serial.flow_control, 1),
             DEFINE_PROP_END_OF_LIST(),
         },
         .qdev.reset = virtio_pci_reset,
diff --git a/hw/virtio-serial-bus.c b/hw/virtio-serial-bus.c
index 1753785..f681646 100644
--- a/hw/virtio-serial-bus.c
+++ b/hw/virtio-serial-bus.c
@@ -49,6 +49,8 @@ struct VirtIOSerial {
     uint32_t *ports_map;
 
     struct virtio_console_config config;
+
+    bool flow_control;
 };
 
 static VirtIOSerialPort *find_port_by_id(VirtIOSerial *vser, uint32_t id)
@@ -123,12 +125,46 @@ static void discard_vq_data(VirtQueue *vq, VirtIODevice 
*vdev)
     virtio_notify(vdev, vq);
 }
 
+static void do_flush_queued_data_no_flow_control(VirtIOSerialPort *port,
+                                                 VirtQueue *vq,
+                                                 VirtIODevice *vdev)
+{
+    VirtQueueElement elem;
+
+    while (!port->throttled && virtqueue_pop(vq, &elem)) {
+        uint8_t *buf;
+        size_t ret, buf_size;
+
+        buf_size = iov_size(elem.out_sg, elem.out_num);
+        buf = qemu_malloc(buf_size);
+        ret = iov_to_buf(elem.out_sg, elem.out_num, buf, 0, buf_size);
+
+        /*
+         * have_data has been modified to return the number of bytes
+         * successfully consumed.  We can't act upon that information
+         * in the no-flow-control implementation, so we'll discard it
+         * here.  No callers currently use flow control, but they
+         * should take this into account for backward compatibility.
+         */
+        port->info->have_data(port, buf, ret);
+        qemu_free(buf);
+
+        virtqueue_push(vq, &elem, 0);
+    }
+    virtio_notify(vdev, vq);
+}
+
 static void do_flush_queued_data(VirtIOSerialPort *port, VirtQueue *vq,
                                  VirtIODevice *vdev)
 {
     assert(port);
     assert(virtio_queue_ready(vq));
 
+    if (!virtio_serial_flow_control_enabled(port)) {
+        do_flush_queued_data_no_flow_control(port, vq, vdev);
+        return;
+    }
+
     while (!port->throttled) {
         unsigned int i;
 
@@ -296,6 +332,15 @@ void virtio_serial_throttle_port(VirtIOSerialPort *port, 
bool throttle)
     flush_queued_data(port);
 }
 
+bool virtio_serial_flow_control_enabled(VirtIOSerialPort *port)
+{
+    if (!port) {
+        return false;
+    }
+
+    return port->vser->flow_control;
+}
+
 /* Guest wants to notify us of some event */
 static void handle_control_message(VirtIOSerial *vser, void *buf, size_t len)
 {
@@ -533,17 +578,19 @@ static void virtio_serial_save(QEMUFile *f, void *opaque)
         qemu_put_byte(f, port->guest_connected);
         qemu_put_byte(f, port->host_connected);
 
-       elem_popped = 0;
-        if (port->elem.out_num) {
-            elem_popped = 1;
-        }
-        qemu_put_be32s(f, &elem_popped);
-        if (elem_popped) {
-            qemu_put_be32s(f, &port->iov_idx);
-            qemu_put_be64s(f, &port->iov_offset);
+        if (virtio_serial_flow_control_enabled(port)) {
+            elem_popped = 0;
+            if (port->elem.out_num) {
+                elem_popped = 1;
+            }
+            qemu_put_be32s(f, &elem_popped);
+            if (elem_popped) {
+                qemu_put_be32s(f, &port->iov_idx);
+                qemu_put_be64s(f, &port->iov_offset);
 
-            qemu_put_buffer(f, (unsigned char *)&port->elem,
-                            sizeof(port->elem));
+                qemu_put_buffer(f, (unsigned char *)&port->elem,
+                                sizeof(port->elem));
+            }
         }
     }
 }
@@ -816,6 +863,7 @@ VirtIODevice *virtio_serial_init(DeviceState *dev, 
virtio_serial_conf *conf)
     VirtIOSerial *vser;
     VirtIODevice *vdev;
     uint32_t i, max_supported_ports;
+    unsigned int savevm_ver;
 
     if (!conf->max_virtserial_ports)
         return NULL;
@@ -881,11 +929,18 @@ VirtIODevice *virtio_serial_init(DeviceState *dev, 
virtio_serial_conf *conf)
 
     vser->qdev = dev;
 
+    vser->flow_control = true;
+    savevm_ver = 3;
+    if (!conf->flow_control) {
+        vser->flow_control = false;
+        savevm_ver = 2;
+    }
+
     /*
      * Register for the savevm section with the virtio-console name
      * to preserve backward compat
      */
-    register_savevm(dev, "virtio-console", -1, 3, virtio_serial_save,
+    register_savevm(dev, "virtio-console", -1, savevm_ver, virtio_serial_save,
                     virtio_serial_load, vser);
 
     return vdev;
diff --git a/hw/virtio-serial.h b/hw/virtio-serial.h
index de624c3..57d2dee 100644
--- a/hw/virtio-serial.h
+++ b/hw/virtio-serial.h
@@ -48,6 +48,13 @@ struct virtio_console_control {
 struct virtio_serial_conf {
     /* Max. number of ports we can have for a the virtio-serial device */
     uint32_t max_virtserial_ports;
+
+    /*
+     * Should this device behave the way it did in prior to pc-0.14
+     * (ie. no flow control)?  This will be necessary to allow
+     * migrations from a pre-0.14-machine type to older qemu code
+     */
+    uint32_t flow_control;
 };
 
 /* Some events for the internal messages (control packets) */
@@ -204,4 +211,9 @@ size_t virtio_serial_guest_ready(VirtIOSerialPort *port);
  */
 void virtio_serial_throttle_port(VirtIOSerialPort *port, bool throttle);
 
+/*
+ * Does this machine type disable the use of flow control?
+ */
+bool virtio_serial_flow_control_enabled(VirtIOSerialPort *port);
+
 #endif
-- 
1.7.3.5