spice-qemu-char: Generate chardev open/close events

Define a state callback and make that generate chardev open/close events when
called by the spice-server.

Notes:

1) For all but the newest spice-server versions (which have a fix for this)
the code ignores these events for a spicevmc with a subtype of vdagent, this
subtype specific knowledge is undesirable, but unavoidable for now, see:
http://lists.freedesktop.org/archives/spice-devel/2011-July/004837.html

2) This code deliberately sends the events immediately rather then from a
bh. This is done this way because:
a) There is no need to do it from a bh; and
b) Doing it from a bh actually causes issues because the spice-server may send
data immediately after the open and when the open runs from a bh, then
qemu_chr_be_can_write will return 0 for the first write which the spice-server
does not expect, when this happens the spice-server will never retry the write
causing communication to stall.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

spice-qemu-char.c

@@ -69,11 +69,40 @@ static int vmc_read(SpiceCharDeviceInstance *sin, uint8_t *buf, int len)
     return bytes;
 }
 
+static void vmc_state(SpiceCharDeviceInstance *sin, int connected)
+{
+    SpiceCharDriver *scd = container_of(sin, SpiceCharDriver, sin);
+
+#if SPICE_SERVER_VERSION < 0x000901
+    /*
+     * spice-server calls the state callback for the agent channel when the
+     * spice client connects / disconnects. Given that not the client but
+     * the server is doing the parsing of the messages this is wrong as the
+     * server is still listening. Worse, this causes the parser in the server
+     * to go out of sync, so we ignore state calls for subtype vdagent
+     * spicevmc chardevs. For the full story see:
+     * http://lists.freedesktop.org/archives/spice-devel/2011-July/004837.html
+     */
+    if (strcmp(sin->subtype, "vdagent") == 0) {
+        return;
+    }
+#endif
+
+    if ((scd->chr->opened && connected) ||
+        (!scd->chr->opened && !connected)) {
+        return;
+    }
+
+    qemu_chr_be_event(scd->chr,
+                      connected ? CHR_EVENT_OPENED : CHR_EVENT_CLOSED);
+}
+
 static SpiceCharDeviceInterface vmc_interface = {
     .base.type          = SPICE_INTERFACE_CHAR_DEVICE,
     .base.description   = "spice virtual channel char device",
     .base.major_version = SPICE_INTERFACE_CHAR_DEVICE_MAJOR,
     .base.minor_version = SPICE_INTERFACE_CHAR_DEVICE_MINOR,
+    .state              = vmc_state,
     .write              = vmc_write,
     .read               = vmc_read,
 };
@@ -197,7 +226,12 @@ int qemu_chr_open_spice(QemuOpts *opts, CharDriverState **_chr)
     chr->chr_guest_open = spice_chr_guest_open;
     chr->chr_guest_close = spice_chr_guest_close;
 
-    qemu_chr_generic_open(chr);
+#if SPICE_SERVER_VERSION < 0x000901
+    /* See comment in vmc_state() */
+    if (strcmp(subtype, "vdagent") == 0) {
+        qemu_chr_generic_open(chr);
+    }
+#endif
 
     *_chr = chr;
     return 0;