virtio-serial: enable virtio console emergency write feature

Add support for enabling the virtio 1.0 "emergency write"
(VIRTIO_CONSOLE_F_EMERG_WRITE) feature. The previous patch introduced
the plumbing required for this; now we expose the virtio feature to
the guest. The feature is disabled for compatibility machines to avoid
exposing a new feature to existing guests.

As required by the virtio 1.0 spec, the emergency write functionality
is available to the guest even if the guest doesn't negotatiate the
feature, as well as before feature negotation.

Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
index 57419b2b6a0026e49c71c1a077b21da2d5e87591..db2a9f19bc2e2bdd7dd6c4f3251aa5f6b2ab5a71 100644 (file)
--- a/hw/char/virtio-serial-bus.c
+++ b/hw/char/virtio-serial-bus.c
@@ -541,6 +541,7 @@ static uint64_t get_features(VirtIODevice *vdev, uint64_t features,
 
     vser = VIRTIO_SERIAL(vdev);
 
+    features |= vser->host_features;
     if (vser->bus.max_nr_ports > 1) {
         virtio_add_feature(&features, VIRTIO_CONSOLE_F_MULTIPORT);
     }
@@ -1003,6 +1004,7 @@ static void virtio_serial_device_realize(DeviceState *dev, Error **errp)
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
     VirtIOSerial *vser = VIRTIO_SERIAL(dev);
     uint32_t i, max_supported_ports;
+    size_t config_size = sizeof(struct virtio_console_config);
 
     if (!vser->serial.max_virtserial_ports) {
         error_setg(errp, "Maximum number of serial ports not specified");
@@ -1017,10 +1019,12 @@ static void virtio_serial_device_realize(DeviceState *dev, Error **errp)
         return;
     }
 
-    /* We don't support emergency write, skip it for now. */
-    /* TODO: cleaner fix, depending on host features. */
+    if (!virtio_has_feature(vser->host_features,
+                            VIRTIO_CONSOLE_F_EMERG_WRITE)) {
+        config_size = offsetof(struct virtio_console_config, emerg_wr);
+    }
     virtio_init(vdev, "virtio-serial", VIRTIO_ID_CONSOLE,
-                offsetof(struct virtio_console_config, emerg_wr));
+                config_size);
 
     /* Spawn a new virtio-serial bus on which the ports will ride as devices */
     qbus_create_inplace(&vser->bus, sizeof(vser->bus), TYPE_VIRTIO_SERIAL_BUS,
@@ -1116,6 +1120,8 @@ VMSTATE_VIRTIO_DEVICE(console, 3, virtio_serial_load, virtio_vmstate_save);
 static Property virtio_serial_properties[] = {
     DEFINE_PROP_UINT32("max_ports", VirtIOSerial, serial.max_virtserial_ports,
                                                   31),
+    DEFINE_PROP_BIT64("emergency-write", VirtIOSerial, host_features,
+                      VIRTIO_CONSOLE_F_EMERG_WRITE, true),
     DEFINE_PROP_END_OF_LIST(),
 };
 

diff --git a/include/hw/compat.h b/include/hw/compat.h
index 46412b229a706331f42ef4f98b7554b204ac6dc3..ef3fae3e1beaccdd89d815497e741dccae7eeb8d 100644 (file)
--- a/include/hw/compat.h
+++ b/include/hw/compat.h
@@ -6,6 +6,10 @@
         .driver   = "virtio-pci",\
         .property = "page-per-vq",\
         .value    = "on",\
+    },{\
+        .driver   = "virtio-serial-device",\
+        .property = "emergency-write",\
+        .value    = "off",\
     },{\
         .driver   = "ioapic",\
         .property = "version",\

diff --git a/include/hw/virtio/virtio-serial.h b/include/hw/virtio/virtio-serial.h
index 730c88d2a7805160fcdd1bbfb6a4e0ea6c82b90a..b19c44727f5aa02d4658672315859852756a2101 100644 (file)
--- a/include/hw/virtio/virtio-serial.h
+++ b/include/hw/virtio/virtio-serial.h
@@ -184,6 +184,8 @@ struct VirtIOSerial {
     struct VirtIOSerialPostLoad *post_load;
 
     virtio_serial_conf serial;
+
+    uint64_t host_features;
 };
 
 /* Interface to the virtio-serial bus */