static void vnc_set_share_mode(VncState *vs, VncShareMode mode)
{
#ifdef _VNC_DEBUG
    static const char *mn[] = {
        [0]                           = "undefined",
        [VNC_SHARE_MODE_CONNECTING]   = "connecting",
        [VNC_SHARE_MODE_SHARED]       = "shared",
        [VNC_SHARE_MODE_EXCLUSIVE]    = "exclusive",
        [VNC_SHARE_MODE_DISCONNECTED] = "disconnected",
    };
    fprintf(stderr, "%s/%d: %s -> %s\n", __func__,
            vs->csock, mn[vs->share_mode], mn[mode]);
#endif

    if (vs->share_mode == VNC_SHARE_MODE_EXCLUSIVE) {
        vs->vd->num_exclusive--;
    }
    vs->share_mode = mode;
    if (vs->share_mode == VNC_SHARE_MODE_EXCLUSIVE) {
        vs->vd->num_exclusive++;
    }
}