New API function isoburn_disc_available_space() fixes bug with DVD+RW capacity

libisoburn/libisoburn.h

@@ -654,6 +654,21 @@ int isoburn_set_read_pacifier(struct burn_drive *drive,
 int isoburn_attach_image(struct burn_drive *d, IsoImage *image);
 
 
+/** Return the best possible estimation of the currently available capacity of
+    the media. This might depend on particular write option settings and on
+    drive state.
+    An eventual start address for emulated multi-session will be subtracted
+    from the capacity estimation given by burn_disc_available_space().
+    Negative results get defaulted to 0.
+    Wrapper for: burn_disc_available_space()
+    @param d The drive to query.
+    @param o If not NULL: write parameters to be set on drive before query
+    @return number of most probably available free bytes
+*/
+off_t isoburn_disc_available_space(struct burn_drive *d,
+                                   struct burn_write_opts *o);
+
+
 /** Obtain the start block number of the most recent session on media. In
     case of random access media this will always be 0. Succesfull return is
     not a guarantee that there is a ISO-9660 image at all. The call will fail,