From a2c2a595f2588a53b7c804e688f459e8a1c5efaf Mon Sep 17 00:00:00 2001
From: "Eric S. Raymond" <esr@thyrsus.com>
Date: Fri, 25 Mar 2011 15:01:49 -0400
Subject: First cut at shared-memory export.  Daemon-side only.

Not configured in by default yet because it produces a strange regression
failure.
---
 shmexport.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 shmexport.c

(limited to 'shmexport.c')

diff --git a/shmexport.c b/shmexport.c
new file mode 100644
index 00000000..b9c330c4
--- /dev/null
+++ b/shmexport.c
@@ -0,0 +1,79 @@
+/****************************************************************************
+
+NAME
+   shmexport.c - shared-memory exports from the daemon and how to read them
+
+DESCRIPTION
+   
+
+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
+bool shm_acquire(struct gps_context_t *context)
+/* initialize the shared-memory segment to be used for export */
+{
+    int shmid;
+
+    shmid = shmget((key_t)GPSD_KEY, sizeof(struct gps_data_t), (int)(IPC_CREAT|0666));
+    if (shmid == -1) {
+	gpsd_report(LOG_ERROR, "shmget(%ld, %zd, 0666) failed: %s\n",
+		    (long int)GPSD_KEY, 
+		    sizeof(struct gps_data_t),
+		    strerror(errno));
+	return false;
+    } 
+    context->shmexport = (char *)shmat(shmid, 0, 0);
+    /*@ -mustfreefresh */
+    if ((int)(long)context->shmexport == -1) {
+	gpsd_report(LOG_ERROR, "shmat failed: %s\n", strerror(errno));
+	context->shmexport = NULL;
+	return false;
+    }
+    gpsd_report(LOG_PROG, "shmat() succeeded, segment %d\n", shmid);
+    return true;
+}
+
+void shm_release(struct gps_context_t *context)
+/* release the shared-memory segment used for export */
+{
+    if (context->shmexport != NULL)
+	(void)shmdt((const void *)context->shmexport);
+}
+
+void shm_update(struct gps_context_t *context, struct gps_data_t *gpsdata)
+/* export an update to all listeners */
+{
+    if (context->shmexport != NULL)
+    {
+	static int tick;
+
+	++tick;
+	/*
+	 * Following block of instructions must not be reordered, otherwise 
+	 * havoc will ensue.  asm volatile("sfence") is a GCCism intended
+	 * to prevent reordering.
+	 */
+	((struct shmexport_t *)context)->bookend2 = tick;
+	asm volatile("sfence");
+	memcpy((void *)(context->shmexport + offsetof(struct shmexport_t, gpsdata)),
+	       (void *)gpsdata,
+	       sizeof(struct gps_data_t)); 
+	asm volatile("sfence");
+	((struct shmexport_t *)context)->bookend1 = tick;
+    }
+}
+#endif /* SHM_EXPORT_ENABLE */
+
+/* end */
-- 
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