[Spice-devel] [PATCH v2] Don't close all but one display during reboot.

[Jonathon Jongsma]

When a guest is rebooted, the QXL driver gets unloaded at some point in
the reboot process. When the driver is unloaded, the spice server sets a
single flag to FALSE: RedWorker::driver_cap_monitors_config. This flag
indicates whether the driver is capable of sending its own monitors config
messages to the client.

The only place this flag is used is when a new primary surface is created. If
this flag is true, the server assumes that the driver will send its own
monitors config very soon after the surface is created. If it's false, the
server directly sends its own temporary monitors config message to the client
based on the size of the just-created primary surface. This temporary monitors
config message always has a maximum monitor count of 1.

This flag is set to false at startup so that in early boot (e.g. vga text
mode), the server will send out these 'temporary' monitor config messages to
the client whenever the primary surface is destroyed and re-created. This
causes the client to resize its window to match the size of the guest. When the
QXL driver is loaded and starts taking over the monitors config
responsibilities, we set this flag to true and the server stops sending
monitors config messages out on its own.

If we reboot and set thsi flag to false, it will result in the server sending a
monitors config message to the client indicating that the guest now supports a
maximum of 1 monitor. If the guest happens to have more than one display window
open, it will destroy those extra windows because they exceed the maximum
allowed number of monitors. This means that if you reboot a guest with 4
monitors, after reboot it will only have 1 monitor.

To avoid this, we assume that if we had the ability to support multiple
monitors at some point, that will return at some point. So when the server
constructs its own monitors config message to send to the client (when the
driver_cap_monitors_config flag is false), we send the previous maximum monitor
count instead of always sending a maximum of 1.

Resolves: rhbz#1274447
---

I'm simply re-sending this patch to see if anybody has additional opinions on
this patch. It is clearly a workaround, and there was some skepticism about the
approach when I initially proposed it. I did answer several concerns voiced by
people but the discussion sort of petered out without a conclusion. I'm hoping
to get a firm ACK or NACK on the patch.


 server/display-channel.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/server/display-channel.c b/server/display-channel.c
index bfff413..3864419 100644
--- a/server/display-channel.c
+++ b/server/display-channel.c
@@ -2447,15 +2447,18 @@ void display_channel_set_monitors_config_to_primary(DisplayChannel *display)
 {
     DrawContext *context = &display->priv->surfaces[0].context;
     QXLHead head = { 0, };
+    uint16_t old_max = 1;
 
     spice_return_if_fail(display->priv->surfaces[0].context.canvas);
 
-    if (display->priv->monitors_config)
+    if (display->priv->monitors_config) {
+        old_max = display->priv->monitors_config->max_allowed;
         monitors_config_unref(display->priv->monitors_config);
+    }
 
     head.width = context->width;
     head.height = context->height;
-    display->priv->monitors_config = monitors_config_new(&head, 1, 1);
+    display->priv->monitors_config = monitors_config_new(&head, 1, old_max);
 }
 
 void display_channel_reset_image_cache(DisplayChannel *self)
-- 
2.9.3