[Qemu-devel] [PATCHv3 2/2] virtio-serial: Don't keep a persistent copy of config space

[David Gibson]

The 'config' field in the VirtIOSerial structure keeps a copy of the virtio
console's config space as visible to the guest, that is to say, in guest
endianness.  This is fiddly to maintain, because on some targets, such as
powerpc, the "guest endianness" can change when a new guest OS boots.

In fact, there's no need to maintain such a guest view of config space -
instead we can reconstruct it from host-format data when it is accessed
with get_config.

Signed-off-by: David Gibson <address@hidden>
---
 hw/char/virtio-serial-bus.c       | 29 ++++++++++++++---------------
 include/hw/virtio/virtio-serial.h |  2 --
 2 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/hw/char/virtio-serial-bus.c b/hw/char/virtio-serial-bus.c
index e013504..37a6f44 100644
--- a/hw/char/virtio-serial-bus.c
+++ b/hw/char/virtio-serial-bus.c
@@ -482,10 +482,14 @@ static uint32_t get_features(VirtIODevice *vdev, uint32_t 
features)
 /* Guest requested config info */
 static void get_config(VirtIODevice *vdev, uint8_t *config_data)
 {
-    VirtIOSerial *vser;
-
-    vser = VIRTIO_SERIAL(vdev);
-    memcpy(config_data, &vser->config, sizeof(struct virtio_console_config));
+    VirtIOSerial *vser = VIRTIO_SERIAL(vdev);
+    struct virtio_console_config *config =
+        (struct virtio_console_config *)config_data;
+
+    config->cols = 0;
+    config->rows = 0;
+    config->max_nr_ports = virtio_tswap32(vdev,
+                                          vser->serial.max_virtserial_ports);
 }
 
 static void guest_reset(VirtIOSerial *vser)
@@ -533,10 +537,6 @@ static void vser_reset(VirtIODevice *vdev)
 
     vser = VIRTIO_SERIAL(vdev);
     guest_reset(vser);
-
-    /* In case we have switched endianness */
-    vser->config.max_nr_ports =
-        virtio_tswap32(vdev, vser->serial.max_virtserial_ports);
 }
 
 static void virtio_serial_save(QEMUFile *f, void *opaque)
@@ -551,12 +551,13 @@ static void virtio_serial_save_device(VirtIODevice *vdev, 
QEMUFile *f)
     VirtIOSerialPort *port;
     uint32_t nr_active_ports;
     unsigned int i, max_nr_ports;
+    struct virtio_console_config config;
 
-    /* The config space */
-    qemu_put_be16s(f, &s->config.cols);
-    qemu_put_be16s(f, &s->config.rows);
-
-    qemu_put_be32s(f, &s->config.max_nr_ports);
+    /* The config space (ignored on the far end in current versions) */
+    get_config(vdev, (uint8_t *)&config);
+    qemu_put_be16s(f, &config.cols);
+    qemu_put_be16s(f, &config.rows);
+    qemu_put_be32s(f, &config.max_nr_ports);
 
     /* The ports map */
     max_nr_ports = s->serial.max_virtserial_ports;
@@ -987,8 +988,6 @@ static void virtio_serial_device_realize(DeviceState *dev, 
Error **errp)
         vser->ovqs[i] = virtio_add_queue(vdev, 128, handle_output);
     }
 
-    vser->config.max_nr_ports =
-        virtio_tswap32(vdev, vser->serial.max_virtserial_ports);
     vser->ports_map = g_malloc0(((vser->serial.max_virtserial_ports + 31) / 32)
         * sizeof(vser->ports_map[0]));
     /*
diff --git a/include/hw/virtio/virtio-serial.h 
b/include/hw/virtio/virtio-serial.h
index a679e54..11af978 100644
--- a/include/hw/virtio/virtio-serial.h
+++ b/include/hw/virtio/virtio-serial.h
@@ -207,8 +207,6 @@ struct VirtIOSerial {
     /* bitmap for identifying active ports */
     uint32_t *ports_map;
 
-    struct virtio_console_config config;
-
     struct VirtIOSerialPostLoad *post_load;
 
     virtio_serial_conf serial;
-- 
2.1.0