From 76535a3b3318266b691a12bef71db467be47282d Mon Sep 17 00:00:00 2001
From: "Eric S. Raymond" <esr@thyrsus.com>
Date: Thu, 29 Jan 2015 12:49:06 -0500
Subject: Add a minimum packet length to every driver.

Length 0 means the minimum is unknown and the driver should use character I/O.
---
 driver_evermore.c   |  1 +
 driver_garmin.c     |  3 +++
 driver_geostar.c    |  1 +
 driver_italk.c      |  1 +
 driver_navcom.c     |  1 +
 driver_nmea2000.c   |  1 +
 driver_oncore.c     |  1 +
 driver_proto.c      |  2 ++
 driver_sirf.c       |  1 +
 driver_superstar2.c |  1 +
 driver_tsip.c       |  1 +
 driver_ubx.c        |  1 +
 driver_zodiac.c     |  1 +
 drivers.c           | 19 +++++++++++++++++++
 gpsd.h-tail         |  1 +
 15 files changed, 36 insertions(+)

diff --git a/driver_evermore.c b/driver_evermore.c
index 132d1db4..92a99044 100644
--- a/driver_evermore.c
+++ b/driver_evermore.c
@@ -637,6 +637,7 @@ const struct gps_type_t driver_evermore =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 10,		/* min packet length for chunked I/O */
 };
 /* *INDENT-ON* */
 #endif /* defined(EVERMORE_ENABLE) && defined(BINARY_ENABLE) */
diff --git a/driver_garmin.c b/driver_garmin.c
index d9d4888d..7450d5f7 100644
--- a/driver_garmin.c
+++ b/driver_garmin.c
@@ -1401,6 +1401,7 @@ const struct gps_type_t driver_garmin_usb_binary_old =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = garmin_time_offset,
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 0;		/* min packet length unknown */
 };
 /* *INDENT-ON* */
 #endif /* __UNUSED__ */
@@ -1431,6 +1432,7 @@ const struct gps_type_t driver_garmin_usb_binary =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = garmin_time_offset,
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 0,		/* min packet length unknown */
 };
 /* *INDENT-ON* */
 
@@ -1460,6 +1462,7 @@ const struct gps_type_t driver_garmin_ser_binary =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = garmin_time_offset,
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 0,		/* min packet length unknown */
 };
 /* *INDENT-ON* */
 
diff --git a/driver_geostar.c b/driver_geostar.c
index 11e9ad78..06b2d563 100644
--- a/driver_geostar.c
+++ b/driver_geostar.c
@@ -640,6 +640,7 @@ const struct gps_type_t driver_geostar =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = geostar_time_offset,
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 24,		/* min packet length for the GeoStar */
 };
 /* *INDENT-ON* */
 
diff --git a/driver_italk.c b/driver_italk.c
index 051376c2..e1cdf483 100644
--- a/driver_italk.c
+++ b/driver_italk.c
@@ -432,6 +432,7 @@ const struct gps_type_t driver_italk =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 30,		/* min packet length for chunked output */
 };
 /* *INDENT-ON* */
 #endif /* defined(ITRAX_ENABLE) && defined(BINARY_ENABLE) */
diff --git a/driver_navcom.c b/driver_navcom.c
index 925b7b61..067aef0b 100644
--- a/driver_navcom.c
+++ b/driver_navcom.c
@@ -1310,6 +1310,7 @@ const struct gps_type_t driver_navcom =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 10,		/* min packet length for chunked I/O */
 };
 /* *INDENT-ON* */
 
diff --git a/driver_nmea2000.c b/driver_nmea2000.c
index 1d25158b..fba3f967 100644
--- a/driver_nmea2000.c
+++ b/driver_nmea2000.c
@@ -1687,6 +1687,7 @@ const struct gps_type_t driver_nmea2000 = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 0,		/* min packet length unknown */
 };
 /* *INDENT-ON* */
 
diff --git a/driver_oncore.c b/driver_oncore.c
index 8cea6e7c..569e1f4d 100644
--- a/driver_oncore.c
+++ b/driver_oncore.c
@@ -520,6 +520,7 @@ const struct gps_type_t driver_oncore = {
 #ifdef TIMEHINT_ENABLE
     .time_offset = oncore_time_offset,		/* NTP offset array */
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 38,		/* min packet length for chunked I/O */
 };
 /* *INDENT-ON* */
 #endif /* defined(ONCORE_ENABLE) && defined(BINARY_ENABLE) */
diff --git a/driver_proto.c b/driver_proto.c
index bbbd7c0d..e8953cf8 100644
--- a/driver_proto.c
+++ b/driver_proto.c
@@ -533,6 +533,8 @@ const struct gps_type_t driver__proto__binary = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = _proto_time_offset,
 #endif /* TIMEHINT_ENABLE */
+    /* minimum length of packet, used for I/O optimization */
+    .minlength       = 0;
 /* *INDENT-ON* */
 };
 #endif /* defined(_PROTO__ENABLE) && defined(BINARY_ENABLE) */
diff --git a/driver_sirf.c b/driver_sirf.c
index 20e7b513..87146ce7 100644
--- a/driver_sirf.c
+++ b/driver_sirf.c
@@ -1590,6 +1590,7 @@ const struct gps_type_t driver_sirf =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = sirf_time_offset,
 #endif /* NTP_SHM_ENABLE */
+    .minlength       = 13,		/* minimum SiRF packet length */
 };
 /* *INDENT-ON* */
 #endif /* defined(SIRF_ENABLE) && defined(BINARY_ENABLE) */
diff --git a/driver_superstar2.c b/driver_superstar2.c
index 94cc3320..95d69cd4 100644
--- a/driver_superstar2.c
+++ b/driver_superstar2.c
@@ -585,6 +585,7 @@ const struct gps_type_t driver_superstar2 = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 65,		/* min packet length for chunked I/O */
 };
 /* *INDENT-ON* */
 #endif /* defined(SUPERSTAR2_ENABLE) && defined(BINARY_ENABLE) */
diff --git a/driver_tsip.c b/driver_tsip.c
index 6134e3d9..994da718 100644
--- a/driver_tsip.c
+++ b/driver_tsip.c
@@ -1281,6 +1281,7 @@ const struct gps_type_t driver_tsip =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = tsip_time_offset,
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 5,		/* min packet length for chunked I/O */
 };
 /* *INDENT-ON* */
 
diff --git a/driver_ubx.c b/driver_ubx.c
index 2f2a7358..260c8523 100644
--- a/driver_ubx.c
+++ b/driver_ubx.c
@@ -992,6 +992,7 @@ const struct gps_type_t driver_ubx = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 17,		/* min packet length for chunked I/O */
 };
 /* *INDENT-ON* */
 #endif /* defined(UBLOX_ENABLE) && defined(BINARY_ENABLE) */
diff --git a/driver_zodiac.c b/driver_zodiac.c
index 2a0e367e..1da18bf4 100644
--- a/driver_zodiac.c
+++ b/driver_zodiac.c
@@ -486,6 +486,7 @@ const struct gps_type_t driver_zodiac =
 #ifdef TIMEHINT_ENABLE
     .time_offset     = zodiac_time_offset,	/* compute NTO fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 40,		/* min packet length for chunked I/O */
 };
 /* *INDENT-ON* */
 
diff --git a/drivers.c b/drivers.c
index 0003ad11..b5c898dc 100644
--- a/drivers.c
+++ b/drivers.c
@@ -16,6 +16,8 @@
 #include "bits.h"		/* for getbeu16(), to extract big-endian words */
 #include "strfuncs.h"
 
+#define NMEA_MINLENGTH	16	/* minimum length of NMEA0183 packet */
+
 ssize_t generic_get(struct gps_device_t *session)
 {
     return packet_get(session->gpsdata.gps_fd, &session->lexer);
@@ -102,6 +104,7 @@ const struct gps_type_t driver_unknown = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength	     = 0,		/* minimum packet length is unknown */
 };
 /* *INDENT-ON* */
 
@@ -272,6 +275,7 @@ const struct gps_type_t driver_nmea0183 = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = NMEA_MINLENGTH,	/* min packet length for chunked I/O */
 };
 /* *INDENT-ON* */
 
@@ -374,6 +378,7 @@ const struct gps_type_t driver_garmin = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = NMEA_MINLENGTH,	/* min packet length for chunked I/O */
 };
 /* *INDENT-ON* */
 #endif /* GARMIN_ENABLE && NMEA_ENABLE */
@@ -437,6 +442,7 @@ const struct gps_type_t driver_ashtech = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength	     = 0,		/* minimum packet length is unknown */
 };
 /* *INDENT-ON* */
 #endif /* ASHTECH_ENABLE */
@@ -489,6 +495,7 @@ const struct gps_type_t driver_fv18 = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = NMEA_MINLENGTH,	/* use NMEA minimum length */
 };
 /* *INDENT-ON* */
 #endif /* FV18_ENABLE */
@@ -544,6 +551,7 @@ const struct gps_type_t driver_gpsclock = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = NMEA_MINLENGTH,	/* use NMEA minimum length */
 };
 /* *INDENT-ON* */
 #endif /* GPSCLOCK_ENABLE */
@@ -600,6 +608,7 @@ static const struct gps_type_t driver_tripmate = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = NMEA_MINLENGTH,	/* use NME0183 minimum langth */
 };
 /* *INDENT-ON* */
 #endif /* TRIPMATE_ENABLE */
@@ -651,6 +660,7 @@ static const struct gps_type_t driver_earthmate = {
 #endif /* CONTROLSEND_ENABLE */
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
+    .minlength	     = 40,		/* use Zodiac minimum langth */
 #endif /* TIMEHINT_ENABLE */
 };
 /*@ -redef @*/
@@ -778,6 +788,7 @@ const struct gps_type_t driver_trueNorth = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = NMEA_MINLENGTH,	/* use NME0183 minimum langth */
 };
 /* *INDENT-ON* */
 #endif
@@ -858,6 +869,7 @@ static const struct gps_type_t driver_oceanServer = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = NMEA_MINLENGTH,	/* use NME0183 minimum langth */
 };
 /* *INDENT-ON* */
 #endif
@@ -926,6 +938,7 @@ static const struct gps_type_t driver_fury = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = NMEA_MINLENGTH,	/* use NME0183 minimum langth */
 };
 /* *INDENT-ON* */
 
@@ -981,6 +994,7 @@ static const struct gps_type_t driver_rtcm104v2 = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = 0,		/* raw I/O - could probably be tuned */
 };
 /* *INDENT-ON* */
 #endif /* RTCM104V2_ENABLE */
@@ -1028,6 +1042,7 @@ static const struct gps_type_t driver_rtcm104v3 = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = 0,		/* raw I/O - could probably be tuned */
 };
 /* *INDENT-ON* */
 #endif /* RTCM104V3_ENABLE */
@@ -1064,6 +1079,7 @@ static const struct gps_type_t driver_garmintxt = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,
 #endif /* TIMEHINT_ENABLE */
+    .minlength     = 0,			/* min packet length unknown */
 };
 /* *INDENT-ON* */
 #endif /* GARMINTXT_ENABLE */
@@ -1160,6 +1176,7 @@ const struct gps_type_t driver_mtk3301 = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,
 #endif /* TIMEHINT_ENABLE */
+    .minlength	    = NMEA_MINLENGTH,	/* use NME0183 minimum langth */
 };
 /* *INDENT-ON* */
 #endif /* MTK3301_ENABLE */
@@ -1403,6 +1420,7 @@ const struct gps_type_t driver_aivdm = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no NTP communication */
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 23,		/* minimum AIVDM packet length */
 };
 /* *INDENT-ON* */
 #endif /* AIVDM_ENABLE */
@@ -1507,6 +1525,7 @@ const struct gps_type_t driver_json_passthrough = {
 #ifdef TIMEHINT_ENABLE
     .time_offset     = NULL,		/* no method for NTP fudge factor */
 #endif /* TIMEHINT_ENABLE */
+    .minlength       = 43,		/* minimum JSON packet length */
 };
 /* *INDENT-ON* */
 
diff --git a/gpsd.h-tail b/gpsd.h-tail
index 6cd760b3..ceb2707f 100644
--- a/gpsd.h-tail
+++ b/gpsd.h-tail
@@ -389,6 +389,7 @@ struct gps_type_t {
 #ifdef TIMEHINT_ENABLE
     /*@null@*/double (*time_offset)(struct gps_device_t *session);
 #endif /* TIMEHINT_ENABLE */
+    int minlength;
 };
 
 /*
-- 
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