Change to using blocking I/O and VTIME.

This addresses the buzzing-select problem, but the cost is that the GPS
regression tests require longer delays and may hang if the delays are too short.

All regression tests pass.

1 files changed, 4 insertions, 20 deletions

diff --git a/serial.c b/serial.c
index 9bc74e13..96dfdd7b 100644
--- a/serial.c
+++ b/serial.c
@@ -450,7 +450,7 @@ int gpsd_serial_open(struct gps_device_t *session)
 			"bluetooth socket connect in progress or again : %s\n",
 			strerror(errno));
         }
-	(void)fcntl(session->gpsdata.gps_fd, F_SETFL, (int)mode | O_NONBLOCK);
+	(void)fcntl(session->gpsdata.gps_fd, F_SETFL, (int)mode);
 	gpsd_report(&session->context->errout, LOG_PROG,
 		    "bluez device open success: %s %s\n",
 		    session->gpsdata.dev.path, strerror(errno));
@@ -459,13 +459,13 @@ int gpsd_serial_open(struct gps_device_t *session)
     {
         if ((session->gpsdata.gps_fd =
 	     open(session->gpsdata.dev.path,
-		      (int)(mode | O_NONBLOCK | O_NOCTTY))) == -1) {
+		      (int)(mode | O_NOCTTY))) == -1) {
             gpsd_report(&session->context->errout, LOG_ERROR,
 			    "device open failed: %s - retrying read-only\n",
 			    strerror(errno));
 	    if ((session->gpsdata.gps_fd =
 		 open(session->gpsdata.dev.path,
-			  O_RDONLY | O_NONBLOCK | O_NOCTTY)) == -1) {
+			  O_RDONLY | O_NOCTTY)) == -1) {
 		gpsd_report(&session->context->errout, LOG_ERROR,
 			    "read-only device open failed: %s\n",
 			    strerror(errno));
@@ -533,25 +533,9 @@ int gpsd_serial_open(struct gps_device_t *session)
 	    return -1;
 	(void)memcpy(&session->ttyset,
 		     &session->ttyset_old, sizeof(session->ttyset));
-	/*
-	 * Only block until we get at least one character, whatever the
-	 * third arg of read(2) says.  According to 
-	 * http://stackoverflow.com/questions/20154157/termios-vmin-vtime-and-blocking-non-blocking-read-operations
-	 * the VMIN setting may be a no-op because the tty was opened with
-	 * O_NONBLOCK.  Money quote:
-	 *
-	 * "When using select() with a file in non-blocking mode, you
-	 * get an event for every byte that arrives. At high serial
-	 * data rates, this hammers the CPU. It's better to use
-	 * blocking mode with VMIN, so that select() waits for a
-	 * block of data before firing an event, and VTIME to limit
-	 * the delay, for blocks smaller than VMIN."
-	 *
-	 * Would that we could do the latter...
-	 */
 	/*@ ignore @*/
 	memset(session->ttyset.c_cc, 0, sizeof(session->ttyset.c_cc));
-	session->ttyset.c_cc[VMIN] = 1;
+	session->ttyset.c_cc[VTIME] = 1;
 	/*@ end @*/
 	/*
 	 * Tip from Chris Kuethe: the FIDI chip used in the Trip-Nav