Never block when opening the port

Whether blocking happens depends on the value of CDC signal and previously
set CLOCAL settings. Since we cannot influence CLOCAL settings before
opening the port, we have to use O_NONBLOCK.

diff --git a/sterm.c b/sterm.c
index e9d914abbb4fc4ae71ff56cce1cc2c432d8412fa..209f83c92df4d42ecd2a13d8c3c58d3e4a2ac73a 100644 (file)
--- a/sterm.c
+++ b/sterm.c
@@ -1,7 +1,7 @@
 /*
  * Simple serial terminal
  *
- * Copyright 2014 Michal Sojka <sojkam1@fel.cvut.cz>
+ * Copyright 2014, 2015 Michal Sojka <sojkam1@fel.cvut.cz>
  *
  * This program is free software: you can redistribute it and/or
  * modify it under the terms of the GNU General Public License as
@@ -209,10 +209,14 @@ int main(int argc, char *argv[])
        }
        atexit(unlock);
 
-       if ((fd = open(dev, O_RDWR)) < 0) {
+       /* O_NONBLOCK is needed to not wait for the CDC signal. See tty_ioctl(4). */
+       if ((fd = open(dev, O_RDWR|O_NOCTTY|O_NONBLOCK)) < 0) {
                perror(dev);
                exit(1);
        }
+        /* Cancel the efect of O_NONBLOCK flag. */
+       int n = fcntl(fd, F_GETFL, 0);
+        fcntl(fd, F_SETFL, n & ~O_NDELAY);
 
        if (isatty(fd)) {
                CHECK(ioctl(fd, TIOCEXCL, NULL));