First cut at read side of shared-memory exporter.

Untested, probably buggy.  All regression tests pass.

1 files changed, 75 insertions, 0 deletions

diff --git a/libgps_shm.c b/libgps_shm.c
new file mode 100644
index 00000000..daf0f632
--- /dev/null
+++ b/libgps_shm.c
@@ -0,0 +1,75 @@
+/****************************************************************************
+
+NAME
+   libgps_shm.c - reasder access to shared-memory export
+
+DESCRIPTION
+   This is a very lightweight alternative to JSON-over-sockets.  Clients
+won't be able to filter by device, and won't get device activation/deactivation
+notifications.  But both client and daemon will avoid all the marshalling and 
+unmarshalling overhead.
+
+PERMISSIONS
+   This file is Copyright (c) 2010 by the GPSD project
+   BSD terms apply: see the file COPYING in the distribution root for details.
+
+***************************************************************************/
+#include <stddef.h>
+#include <string.h>
+#include <errno.h>
+#include <sys/time.h>
+#include <sys/ipc.h>
+#include <sys/shm.h>
+
+#include "gpsd.h"
+
+#ifdef SHM_EXPORT_ENABLE
+
+int gps_shm_open(/*@out@*/struct gps_data_t *gpsdata)
+/* open a shared-memory connection to the daemon */
+{
+    int shmid;
+
+    gpsdata->privdata = NULL;
+    shmid = shmget((key_t)GPSD_KEY, sizeof(struct gps_data_t), 0);
+    if (shmid == -1) {
+	/* daemon isn't running or failed to create shared segment */
+	return -1;
+    } 
+    gpsdata->privdata = shmat(shmid, 0, 0);
+    if ((int)(long)gpsdata->privdata == -1) {
+	/* attach failed for sume unknown reason */
+	return -2;
+    }
+    return 0;
+}
+
+int gps_shm_read(struct gps_data_t *gpsdata)
+/* read an update from the shared-memory segment */
+{
+    if (gpsdata->privdata == NULL)
+	return -1;
+    else
+    {
+	int before, after;
+	struct shmexport_t *shared = (struct shmexport_t *)gpsdata->privdata;
+
+	before = shared->bookend1;
+	(void)memcpy((void *)gpsdata, 
+		     (void *)&shared->gpsdata, 
+		     sizeof(struct gps_data_t));
+	after = shared->bookend2;
+	/*@i1@*/gpsdata->privdata = shared;
+	return (before == after) ? 0 : -1;
+    }
+}
+
+void gps_shm_close(struct gps_data_t *gpsdata)
+{
+    if (gpsdata->privdata != NULL)
+	(void)shmdt((const void *)gpsdata->privdata);
+}
+
+#endif /* SHM_EXPORT_ENABLE */
+
+/* end */