feat: add log format flags

With these flags API consumers can optimize the depiction of libliftoff's debug
log.

For now the two flags for a section start and end are introduced. It is
guaranteed that one section always ends before the next one begins.

Is no callback function setup section starts and ends in the default stderr
output will be marked with an empty line.

BREAKING CHANGE: The signature of the log callback changes.

alloc.c

@@ -570,8 +570,8 @@ static void log_reuse(struct liftoff_output *output)
 
 static void log_no_reuse(struct liftoff_output *output)
 {
-	liftoff_log(LIFTOFF_DEBUG,
+	liftoff_log_formatted(LIFTOFF_DEBUG, LIFTOFF_LOG_SECTION_START,
-				"\n== Apply request for output %"PRIu32" ==", output->crtc_id);
+				"== Apply request for output %"PRIu32" ==", output->crtc_id);
 
 	if (output->alloc_reused_counter != 0) {
 		liftoff_log(LIFTOFF_DEBUG,
@@ -619,7 +619,7 @@ static void log_planes(struct liftoff_device *device,
 	} else {
 		debug_cnt(device, ":");
 	}
-	debug_cnt(device, NULL);
+	debug_end(device, LIFTOFF_LOG_SECTION_START);
 
 	liftoff_list_for_each(plane, &device->planes, link) {
 		bool active = false;
@@ -662,7 +662,7 @@ static void log_planes(struct liftoff_device *device,
 			char *name;
 
 			if (++per_line == max_per_line) {
-				debug_cnt(device, NULL);
+				debug_end(device, 0);
 				debug_cnt(device, "   ");
 				per_line = 0;
 			}
@@ -694,7 +694,7 @@ static void log_planes(struct liftoff_device *device,
 			}
 			debug_cnt(device, " %s: %"PRIu64, name, value);
 		}
-		debug_cnt(device, NULL);
+		debug_end(device, 0);
 	}
 }
 
@@ -704,7 +704,7 @@ static bool reset_planes(struct liftoff_device *device, drmModeAtomicReq *req)
 	uint32_t debug_type = DRM_PLANE_TYPE_PRIMARY;
 	bool compatible;
 
-	debug_cnt(device, "\nReset planes:");
+	debug_cnt(device, "Reset planes:");
 
 	liftoff_list_for_each(plane, &device->planes, link) {
 		if (plane->layer != NULL) {
@@ -721,13 +721,14 @@ static bool reset_planes(struct liftoff_device *device, drmModeAtomicReq *req)
 
 		if (!plane_apply(plane, NULL, req, &compatible)) {
 			debug_cnt(device, "... Error resetting: %"PRIu32, plane->id);
-			debug_cnt(device, NULL);
+			debug_end(device,
+					  LIFTOFF_LOG_SECTION_START | LIFTOFF_LOG_SECTION_END);
 			return false;
 		}
 		assert(compatible);
 	}
 
-	debug_cnt(device, NULL);
+	debug_end(device, LIFTOFF_LOG_SECTION_START | LIFTOFF_LOG_SECTION_END);
 	return true;
 }
 
@@ -806,7 +807,8 @@ bool liftoff_output_apply(struct liftoff_output *output, drmModeAtomicReq *req)
 		    "score=%d:", (void *)output, result.best_score);
 
 	/* Apply the best allocation */
-	liftoff_log(LIFTOFF_DEBUG, "\nFinal assignment of layers to planes:");
+	liftoff_log_formatted(LIFTOFF_DEBUG, LIFTOFF_LOG_SECTION_START,
+						  "Final assignment of layers to planes:");
 	i = j = 0;
 	liftoff_list_for_each(plane, &device->planes, link) {
 		layer = result.best[i];

include/libliftoff.h

@@ -74,7 +74,14 @@ enum liftoff_log_importance {
 	LIFTOFF_DEBUG,
 };
 
+enum liftoff_log_flags {
+	LIFTOFF_LOG_NO_FLAG			= 0,
+	LIFTOFF_LOG_SECTION_START	= 1,
+	LIFTOFF_LOG_SECTION_END		= 2,
+};
+
 typedef void (*liftoff_log_func)(enum liftoff_log_importance importance,
+								 enum liftoff_log_flags flags,
 								 const char *fmt, va_list args);
 
 void liftoff_log_init(enum liftoff_log_importance verbosity,

include/log.h

@@ -13,9 +13,13 @@ bool log_has(enum liftoff_log_importance verbosity);
 
 void liftoff_log(enum liftoff_log_importance verbosity,
 		 const char *format, ...) _LIFTOFF_ATTRIB_PRINTF(2, 3);
+void liftoff_log_formatted(enum liftoff_log_importance verbosity,
+		 enum liftoff_log_flags flags,
+		 const char *format, ...) _LIFTOFF_ATTRIB_PRINTF(3, 4);
 void liftoff_log_errno(enum liftoff_log_importance verbosity, const char *msg);
 
 void debug_cnt(struct liftoff_device *device, const char *format, ...)
 _LIFTOFF_ATTRIB_PRINTF(2, 3);
+void debug_end(struct liftoff_device *device, enum liftoff_log_flags flags);
 
 #endif

log.c

@@ -7,11 +7,18 @@
 
 static enum liftoff_log_importance log_importance = LIFTOFF_ERROR;
 
-static void log_stderr(enum liftoff_log_importance verbosity, const char *fmt,
+static void log_stderr(enum liftoff_log_importance verbosity,
-		       va_list args)
+					   enum liftoff_log_flags flags,
+					   const char *fmt, va_list args)
 {
+	if (flags & LIFTOFF_LOG_SECTION_START) {
+		fprintf(stderr, "\n");
+	}
 	vfprintf(stderr, fmt, args);
 	fprintf(stderr, "\n");
+	if (flags & LIFTOFF_LOG_SECTION_END) {
+		fprintf(stderr, "\n");
+	}
 }
 
 static liftoff_log_func log_callback = log_stderr;
@@ -39,7 +46,21 @@ void liftoff_log(enum liftoff_log_importance verbosity, const char *fmt, ...)
 
 	va_list args;
 	va_start(args, fmt);
-	log_callback(verbosity, fmt, args);
+	log_callback(verbosity, 0, fmt, args);
+	va_end(args);
+}
+
+void liftoff_log_formatted(enum liftoff_log_importance verbosity,
+						   enum liftoff_log_flags flags,
+						   const char *fmt, ...)
+{
+	if (!log_has(verbosity)) {
+		return;
+	}
+
+	va_list args;
+	va_start(args, fmt);
+	log_callback(verbosity, flags, fmt, args);
 	va_end(args);
 }
 
@@ -55,18 +76,6 @@ void debug_cnt(struct liftoff_device *device, const char *fmt, ...)
 		return;
 	}
 
-	if (fmt == NULL) {
-		if (device->log_buf == 0) {
-			return;
-		}
-		liftoff_log(LIFTOFF_DEBUG, "%s", device->log_buf);
-		free(device->log_buf);
-		device->log_buf = NULL;
-		device->log_buf_index = 0;
-		device->log_buf_len = 0;
-		return;
-	}
-
 	va_list args;
 	va_start(args, fmt);
 
@@ -112,3 +121,18 @@ cleanup_out:
 final_out:
 	va_end(args);
 }
+
+void debug_end(struct liftoff_device *device, enum liftoff_log_flags flags)
+{
+	if (!log_has(LIFTOFF_DEBUG)) {
+		return;
+	}
+	if (device->log_buf == NULL) {
+		return;
+	}
+	liftoff_log_formatted(LIFTOFF_DEBUG, flags, "%s", device->log_buf);
+	free(device->log_buf);
+	device->log_buf = NULL;
+	device->log_buf_index = 0;
+	device->log_buf_len = 0;
+}

plane.c

@@ -48,21 +48,21 @@ static void log_plane(struct liftoff_device *device,
 	} else {
 		debug_cnt(device, "Overlay");
 	}
-	debug_cnt(device, NULL);
+	debug_end(device, 0);
 
 	liftoff_log(LIFTOFF_DEBUG, "     zpos: %"PRIu32, plane->zpos);
 
 	debug_cnt(device, "    props:");
 	for (i = 0; i < plane->props_len; i++) {
 		if (per_line == 5) {
-			debug_cnt(device, NULL);
+			debug_end(device, 0);
 			debug_cnt(device, "          ");
 			per_line = 0;
 		}
 		debug_cnt(device, " %s", plane->props[i].name);
 		per_line++;
 	}
-	debug_cnt(device, NULL);
+	debug_end(device, 0);
 }
 
 struct liftoff_plane *plane_create(struct liftoff_device *device, uint32_t id)
@@ -77,7 +77,7 @@ struct liftoff_plane *plane_create(struct liftoff_device *device, uint32_t id)
 	bool has_type = false, has_zpos = false;
 
 	debug_cnt(device, "Plane %"PRIu32, id);
-	debug_cnt(device, NULL);
+	debug_end(device, 0);
 
 	plane = calloc(1, sizeof(*plane));
 	if (plane == NULL) {