Restore framebuffer when switching back to VT

The kernel currently automatically redirects
output to the kernel framebuffer when switching
VTs away from wayland.  It doesn't restore
output back to wayland's fb when coming back
to the VT.  This patch works around that issue.

egl-compositor.c

@@ -38,6 +38,7 @@
 #include <png.h>
 #include <math.h>
 #include <linux/input.h>
+#include <linux/vt.h>
 #include <xf86drmMode.h>
 #include <time.h>
 #include <fnmatch.h>
@@ -76,8 +77,10 @@ struct egl_compositor {
 	EGLSurface surface;
 	EGLContext context;
 	EGLConfig config;
+	uint32_t fb_id;
 	struct wl_display *wl_display;
 	int gem_fd;
+	int tty_fd;
 	int width, height;
 	struct egl_surface *background;
 	struct egl_surface *overlay;
@@ -86,6 +89,9 @@ struct egl_compositor {
 	struct wl_list input_device_list;
 	struct wl_list surface_list;
 
+	struct wl_event_source *enter_vt_source;
+	struct wl_event_source *leave_vt_source;
+
 	/* Repaint state. */
 	struct wl_event_source *timer_source;
 	int repaint_needed;
@@ -860,7 +866,7 @@ egl_device_get_position(struct egl_input_device *device, int32_t *x, int32_t *y)
 }
 
 static uint32_t
-create_frontbuffer(int fd, int *width, int *height, int *stride)
+create_frontbuffer(int fd, int *width, int *height, int *stride, uint32_t *fb_id)
 {
 	drmModeConnector *connector;
 	drmModeRes *resources;
@@ -868,7 +874,6 @@ create_frontbuffer(int fd, int *width, int *height, int *stride)
 	struct drm_mode_modeinfo *mode;
 	struct drm_i915_gem_create create;
 	struct drm_gem_flink flink;
-	unsigned int fb_id;
 	int i, ret;
 
 	resources = drmModeGetResources(fd);
@@ -916,13 +921,13 @@ create_frontbuffer(int fd, int *width, int *height, int *stride)
 	}
 
 	ret = drmModeAddFB(fd, mode->hdisplay, mode->vdisplay,
-			   32, 32, mode->hdisplay * 4, create.handle, &fb_id);
+			   32, 32, mode->hdisplay * 4, create.handle, fb_id);
 	if (ret) {
 		fprintf(stderr, "failed to add fb: %m\n");
 		return 0;
 	}
 
-	ret = drmModeSetCrtc(fd, encoder->crtc_id, fb_id, 0, 0,
+	ret = drmModeSetCrtc(fd, encoder->crtc_id, *fb_id, 0, 0,
 			     &connector->connector_id, 1, mode);
 	if (ret) {
 		fprintf(stderr, "failed to set mode: %m\n");
@@ -1038,6 +1043,93 @@ static const GOptionEntry option_entries[] = {
 	{ NULL }
 };
 
+static void on_enter_vt(int signal_number, void *data)
+{
+	struct egl_compositor *ec = data;
+
+	drmModeConnector *connector;
+	drmModeRes *resources;
+	drmModeEncoder *encoder;
+	struct drm_mode_modeinfo *mode;
+	int i, ret;
+	int fd;
+
+	fd = ec->gem_fd;
+	resources = drmModeGetResources(fd);
+	if (!resources) {
+		fprintf(stderr, "drmModeGetResources failed\n");
+		return;
+	}
+
+	for (i = 0; i < resources->count_connectors; i++) {
+		connector = drmModeGetConnector(fd, resources->connectors[i]);
+		if (connector == NULL)
+			continue;
+
+		if (connector->connection == DRM_MODE_CONNECTED &&
+		    connector->count_modes > 0)
+			break;
+
+		drmModeFreeConnector(connector);
+	}
+
+	if (i == resources->count_connectors) {
+		fprintf(stderr, "No currently active connector found.\n");
+		return;
+	}
+
+	mode = &connector->modes[0];
+
+	for (i = 0; i < resources->count_encoders; i++) {
+		encoder = drmModeGetEncoder(fd, resources->encoders[i]);
+
+		if (encoder == NULL)
+			continue;
+
+		if (encoder->encoder_id == connector->encoder_id)
+			break;
+
+		drmModeFreeEncoder(encoder);
+	}
+
+	ret = drmModeSetCrtc(fd, encoder->crtc_id, ec->fb_id, 0, 0,
+			     &connector->connector_id, 1, mode);
+	if (ret) {
+		fprintf(stderr, "failed to set mode: %m\n");
+		return;
+	}
+
+}
+
+static void on_leave_vt(int signal_number, void *data)
+{
+	struct egl_compositor *ec = data;
+
+	ioctl (ec->tty_fd, VT_RELDISP, 1);
+}
+
+static void watch_for_vt_changes(struct egl_compositor *ec, struct wl_event_loop *loop)
+{
+	int fd;
+	struct vt_mode mode = { 0 };
+
+	ec->tty_fd = open("/dev/tty0", O_RDWR | O_NOCTTY);
+	mode.mode = VT_PROCESS;
+	mode.relsig = SIGUSR1;
+	mode.acqsig = SIGUSR2;
+
+	if (!ioctl (fd, VT_SETMODE, &mode) < 0) {
+		fprintf(stderr, "failed to take control of vt handling\n");
+	}
+
+	ec->leave_vt_source = wl_event_loop_add_signal (loop, SIGUSR1,
+				on_leave_vt,
+				ec);
+	ec->enter_vt_source = wl_event_loop_add_signal (loop, SIGUSR2,
+				on_enter_vt,
+				ec);
+}
+
 static struct egl_compositor *
 egl_compositor_create(struct wl_display *display)
 {
@@ -1071,7 +1163,7 @@ egl_compositor_create(struct wl_display *display)
 		return NULL;
  
 	fb_name = create_frontbuffer(eglGetDisplayFD(ec->display),
-				     &ec->width, &ec->height, &stride);
+				     &ec->width, &ec->height, &stride, &ec->fb_id);
 	ec->surface = eglCreateSurfaceForName(ec->display, ec->config,
 					      fb_name, ec->width, ec->height, stride, attribs);
 	if (ec->surface == NULL) {
@@ -1123,6 +1215,7 @@ egl_compositor_create(struct wl_display *display)
 	wl_display_add_global(display, &shooter->base);
 
 	loop = wl_display_get_event_loop(ec->wl_display);
+	watch_for_vt_changes (ec, loop);
 	ec->timer_source = wl_event_loop_add_timer(loop, repaint, ec);
 	ec->repaint_needed = 0;
 	ec->repaint_on_timeout = 0;