Bidirectional GUI protocol negotiation

This implements GUI protocol v1.4, which includes bidirectional protocol
negotiation.  This means that not only does the agent tell the daemon
what protocol version it supports, the daemon also tells the agent what
protocol version it decided to actually use.  This may be less than the
version supported by the agent.  As a result, a GUI daemon including
this patch may be used with any version of the GUI agent supporting
protocol major version 1, even ones that support higher minor versions
than the daemon does.

Author: DemiMarie

gui-daemon/xside.c

@@ -69,8 +69,8 @@
 /* Supported protocol version */
 
 #define PROTOCOL_VERSION_MAJOR 1
-#define PROTOCOL_VERSION_MINOR 3
-#define PROTOCOL_VERSION (PROTOCOL_VERSION_MAJOR << 16 | PROTOCOL_VERSION_MINOR)
+#define PROTOCOL_VERSION_MINOR 4
+#define PROTOCOL_VERSION(x, y) ((x) << 16 | (y))
 
 #if !(PROTOCOL_VERSION_MAJOR == QUBES_GUID_PROTOCOL_VERSION_MAJOR && \
       PROTOCOL_VERSION_MINOR <= QUBES_GUID_PROTOCOL_VERSION_MINOR)
@@ -1312,7 +1312,7 @@ static int is_special_keypress(Ghandles * g, const XKeyEvent * ev, XID remote_wi
             if (len > 0) {
                 /* MSG_CLIPBOARD_DATA used to use the window field to pass the length
                    of the blob, be aware when working with old implementations. */
-                if (g->agent_version < 0x00010002)
+                if (g->protocol_version < PROTOCOL_VERSION(1, 2))
                     hdr.window = len;
                 else
                     hdr.window = remote_winid;
@@ -3603,6 +3603,10 @@ static void send_xconf(Ghandles * g)
     XWindowAttributes attr;
     if (!XGetWindowAttributes(g->display, g->root_win, &attr))
         errx(1, "Cannot query root window attributes!");
+    if (g->protocol_version >= PROTOCOL_VERSION(1, 4)) {
+        /* Bidirectional protocol negotiation is supported */
+        write_struct(g->vchan, g->protocol_version);
+    }
     xconf.w = _VIRTUALX(attr.width);
     xconf.h = attr.height;
     xconf.depth = attr.depth;
@@ -3621,10 +3625,9 @@ static void get_protocol_version(Ghandles * g)
     version_major = untrusted_version >> 16;
     version_minor = untrusted_version & 0xffff;
 
-    if (version_major == PROTOCOL_VERSION_MAJOR &&
-            version_minor <= PROTOCOL_VERSION_MINOR) {
+    if (version_major == PROTOCOL_VERSION_MAJOR) {
         /* agent is compatible */
-        g->agent_version = version_major << 16 | version_minor;
+        g->protocol_version = PROTOCOL_VERSION(version_major, min(version_minor, PROTOCOL_VERSION_MINOR));
         return;
     }
     if (version_major < PROTOCOL_VERSION_MAJOR) {

gui-daemon/xside.h

@@ -181,7 +181,7 @@ struct _global_handles {
     char vmname[32];    /* name of VM */
     int domid;        /* Xen domain id (GUI) */
     int target_domid;        /* Xen domain id (VM) - can differ from domid when GUI is stubdom */
-    uint32_t agent_version;  /* gui-agent (protocol) version */
+    uint32_t protocol_version;  /* gui-agent (protocol) version */
     char *cmdline_color;    /* color of frame */
     uint32_t label_color_rgb; /* color of the frame in RGB */
     char *cmdline_icon;    /* icon hint for WM */