weston-log-flight-rec: Add a global variable to access the ring buffer

With it add also a function which can be used in an assert()-like
situation to display the contents of the ring buffer. Within gdb
this call also be called if the program is loaded/still loaded into
memory.

The global variable will be used in a later patch to be accessed from a
python gdb script.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

include/libweston/weston-log.h

@@ -126,6 +126,9 @@ struct weston_log_subscription *
 weston_log_subscription_iterate(struct weston_log_scope *scope,
 				struct weston_log_subscription *sub_iter);
 
+void
+weston_log_flight_recorder_display_buffer(FILE *file);
+
 #ifdef  __cplusplus
 }
 #endif

libweston/weston-log-flight-rec.c

@@ -46,6 +46,10 @@ struct weston_ring_buffer {
 	bool overlap;		/**< in case buff overlaps, hint from where to print buf contents */
 };
 
+/** allows easy access to the ring buffer in case of a core dump
+ */
+WL_EXPORT struct weston_ring_buffer *weston_primary_flight_recorder_ring_buffer = NULL;
+
 /** A black box type of stream, used to aggregate data continuously, and
  * when needed, to dump its contents for inspection.
  */
@@ -182,25 +186,36 @@ weston_log_flight_recorder_map_memory(struct weston_debug_log_flight_recorder *f
 		flight_rec->rb.buf[i] = 0xff;
 }
 
-WL_EXPORT void
-weston_log_subscriber_display_flight_rec(struct weston_log_subscriber *sub)
+static void
+weston_log_subscriber_display_flight_rec_data(struct weston_ring_buffer *rb,
+					      FILE *file)
 {
-	struct weston_debug_log_flight_recorder *flight_rec =
-		to_flight_recorder(sub);
-	struct weston_ring_buffer *rb = &flight_rec->rb;
+	FILE *file_d = stderr;
+	if (file)
+		file_d = file;
 
 	if (rb->append_pos <= rb->size && !rb->overlap) {
 		if (rb->append_pos)
-			fwrite(rb->buf, sizeof(char), rb->append_pos, rb->file);
+			fwrite(rb->buf, sizeof(char), rb->append_pos, file_d);
 		else
-			fwrite(rb->buf, sizeof(char), rb->size, rb->file);
+			fwrite(rb->buf, sizeof(char), rb->size, file_d);
 	} else {
 		/* from append_pos to size */
 		fwrite(&rb->buf[rb->append_pos], sizeof(char),
-		       rb->size - rb->append_pos, rb->file);
+		       rb->size - rb->append_pos, file_d);
 		/* from 0 to append_pos */
-		fwrite(rb->buf, sizeof(char), rb->append_pos, rb->file);
+		fwrite(rb->buf, sizeof(char), rb->append_pos, file_d);
+	}
 }
+
+WL_EXPORT void
+weston_log_subscriber_display_flight_rec(struct weston_log_subscriber *sub)
+{
+	struct weston_debug_log_flight_recorder *flight_rec =
+		to_flight_recorder(sub);
+	struct weston_ring_buffer *rb = &flight_rec->rb;
+
+	weston_log_subscriber_display_flight_rec_data(rb, rb->file);
 }
 
 /** Create a flight recorder type of subscriber
@@ -234,6 +249,7 @@ weston_log_subscriber_create_flight_rec(size_t size)
 	}
 
 	weston_ring_buffer_init(&flight_rec->rb, size, weston_rb);
+	weston_primary_flight_recorder_ring_buffer = &flight_rec->rb;
 
 	/* write some data to the rb such that the memory gets mapped */
 	weston_log_flight_recorder_map_memory(flight_rec);
@@ -254,3 +270,22 @@ weston_log_subscriber_destroy_flight_rec(struct weston_log_subscriber *sub)
 	free(flight_rec->rb.buf);
 	free(flight_rec);
 }
+
+/** Retrieve flight recorder ring buffer contents, could be useful when
+ * implementing an assert()-like wrapper.
+ *
+ * @param file a FILE type already opened. Can also pass stderr/stdout under gdb
+ * if the program is loaded into memory.
+ *
+ * Uses the global exposed weston_primary_flight_recorder_ring_buffer.
+ *
+ */
+WL_EXPORT void
+weston_log_flight_recorder_display_buffer(FILE *file)
+{
+	if (!weston_primary_flight_recorder_ring_buffer)
+		return;
+
+	weston_log_subscriber_display_flight_rec_data(weston_primary_flight_recorder_ring_buffer,
+						      file);
+}