uterm: add uterm_video_available() helper

This helper provides information whether a given backend is available and
even whether kernel-runtime support is available for this backend.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>

src/uterm.h

@@ -170,6 +170,7 @@ typedef void (*uterm_display_cb) (struct uterm_display *disp,
 /* misc */
 
 const char *uterm_dpms_to_name(int dpms);
+bool uterm_video_available(unsigned int type);
 
 /* screen interface */
 

src/uterm_video.c

@@ -59,6 +59,29 @@ const char *uterm_dpms_to_name(int dpms)
 	}
 }
 
+bool uterm_video_available(unsigned int type)
+{
+	switch (type) {
+	case UTERM_VIDEO_DRM:
+#ifdef BUILD_ENABLE_VIDEO_DRM
+		return video_drm_available();
+#endif
+		return false;
+	case UTERM_VIDEO_DUMB:
+#ifdef BUILD_ENABLE_VIDEO_DUMB
+		return video_drm_available();
+#endif
+		return false;
+	case UTERM_VIDEO_FBDEV:
+#ifdef BUILD_ENABLE_VIDEO_FBDEV
+		return true;
+#endif
+		return false;
+	default:
+		return false;
+	}
+}
+
 /* Until we allow multiple displays in one screen, we use this constructor which
  * is basically just a wrapper around "struct uterm_dispaly".
  * The idea behind screens is having one single drawing-target which is spread

src/uterm_video.h

@@ -466,6 +466,11 @@ static inline void video_drm_free_name(char *name)
 	free(name);
 }
 
+static inline bool video_drm_available(void)
+{
+	return drmAvailable();
+}
+
 #else
 
 static inline char *video_drm_get_id(int fd)
@@ -486,6 +491,11 @@ static inline void video_drm_free_name(char *name)
 {
 }
 
+bool video_drm_available(void)
+{
+	return false;
+}
+
 #endif
 
 #endif /* UTERM_VIDEO_H */