diff --git a/src/common/execio.h b/src/common/execio.h
--- a/src/common/execio.h
+++ b/src/common/execio.h
@@ -51,11 +51,11 @@ struct execio
 int execio_open(struct execio **rem, const char *progname, char *const argv[]);
 
 /* 
-   blocks, 
-   returns 0 if len is 0. Otherwise, only returns 0 on error/EOF: use execio_state() to determine
+   doesn't block, 
+   returns 0 on success, 1 on failure
 */
-size_t execio_read(struct execio *eio, void *buf, size_t len);
-size_t execio_write(struct execio *eio, void *buf, size_t len);
+int execio_read(struct execio *eio, void *buf, size_t len, size_t *bytesread);
+int execio_write(struct execio *eio, void *buf, size_t len, size_t *bytesread);
 
 enum execio_state execio_state(struct execio *eio);