Add message queue facilities. Each IsoImage will have its own msg queue.

src/libisofs.h

@@ -409,4 +409,53 @@ int iso_dir_iter_take(IsoDirIter *iter);
  */
 int iso_dir_iter_remove(IsoDirIter *iter);
 
+#define ISO_MSGS_MESSAGE_LEN 4096
+
+/** 
+ * Control queueing and stderr printing of messages from a given IsoImage.
+ * Severity may be one of "NEVER", "FATAL", "SORRY", "WARNING", "HINT",
+ * "NOTE", "UPDATE", "DEBUG", "ALL".
+ * 
+ * @param image          The image
+ * @param queue_severity Gives the minimum limit for messages to be queued.
+ *                       Default: "NEVER". If you queue messages then you
+ *                       must consume them by iso_msgs_obtain().
+ * @param print_severity Does the same for messages to be printed directly
+ *                       to stderr.
+ * @param print_id       A text prefix to be printed before the message.
+ * @return               >0 for success, <=0 for error
+ */
+int iso_image_set_msgs_severities(IsoImage *img, char *queue_severity,
+                                 char *print_severity, char *print_id);
+/** 
+ * Obtain the oldest pending message from a IsoImage message queue which has at
+ * least the given minimum_severity. This message and any older message of
+ * lower severity will get discarded from the queue and is then lost forever.
+ * 
+ * Severity may be one of "NEVER", "FATAL", "SORRY", "WARNING", "HINT",
+ * "NOTE", "UPDATE", "DEBUG", "ALL". To call with minimum_severity "NEVER"
+ * will discard the whole queue.
+ * 
+ * @param image      The image whose messages we want to obtain
+ * @param error_code Will become a unique error code as listed in messages.h
+ * @param msg_text   Must provide at least ISO_MSGS_MESSAGE_LEN bytes.
+ * @param os_errno   Will become the eventual errno related to the message
+ * @param severity   Will become the severity related to the message and
+ *                   should provide at least 80 bytes.
+ * @return 1 if a matching item was found, 0 if not, <0 for severe errors
+ */
+int iso_image_obtain_msgs(IsoImage *image, char *minimum_severity,
+                          int *error_code, char msg_text[], int *os_errno,
+                          char severity[]);
+
+/**
+ * Return the messenger object handle used by the given image. This handle
+ * may be used by related libraries to replace their own compatible
+ * messenger objects and thus to direct their messages to the libisofs
+ * message queue. See also: libburn, API function burn_set_messenger().
+ * 
+ * @return the handle. Do only use with compatible
+ */
+void *iso_image_get_messenger(IsoImage *image);
+
 #endif /*LIBISO_LIBISOFS_H_*/