+int gzopen(const char *zpath, int oflags, FILE **f_r, pid_t *pid_r,
+ const char *gziplevel /* 0 for read; may be 0, or "-1" etc. */);
+ /* returns errno value from open */
+void gzclose(FILE **f, pid_t *p, const char *what);
+ /* also OK with f==0, or p==-1 */