serial: Open devie in non-blocking mode and then switch to blocking

There are some serial ports that apparently block during the open in
some circumstances.  We don't want that.  We want to either open it
immediately, or fail fast.

Change-Id: I626b138574bc50f4f4b09c4d609f3623ff512dff

1 files changed, 17 insertions, 3 deletions

diff --git a/src/serial.c b/src/serial.c
index 66ee7564..44032263 100644
--- a/src/serial.c
+++ b/src/serial.c
@@ -59,16 +59,30 @@
 int
 osmo_serial_init(const char *dev, speed_t baudrate)
 {
-	int rc, fd=0, v24;
+	int rc, fd=0, v24, flags;
 	struct termios tio;
 
-	/* Open device */
-	fd = open(dev, O_RDWR | O_NOCTTY);
+	/* Use nonblock as the device might block otherwise */
+	fd = open(dev, O_RDWR | O_NOCTTY | O_SYNC | O_NONBLOCK);
 	if (fd < 0) {
 		dbg_perror("open");
 		return -errno;
 	}
 
+	/* now put it into blcoking mode */
+	flags = fcntl(fd, F_GETFL, 0);
+	if (flags < 0) {
+		dbg_perror("fcntl get flags");
+		return -1;
+	}
+
+	flags &= ~O_NONBLOCK;
+	rc = fcntl(fd, F_SETFL, flags);
+	if (rc != 0) {
+		dbg_perror("fcntl set flags");
+		return -1;
+	}
+
 	/* Configure serial interface */
 	rc = tcgetattr(fd, &tio);
 	if (rc < 0) {