extern int setup_revisions(int argc, const char **argv, struct rev_info *revs, const char *def);
extern int handle_revision_arg(const char *arg, struct rev_info *revs,int flags,int cant_be_filename);
-extern void prepare_revision_walk(struct rev_info *revs);
+extern int prepare_revision_walk(struct rev_info *revs);
extern struct commit *get_revision(struct rev_info *revs);
extern void mark_parents_uninteresting(struct commit *commit);