X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=blobdiff_plain;f=ipc.c;h=89bbe53564e3c678e97b453e38b7c70be8063314;hp=c1069ad9af067a026c794663be96518351eec8ee;hb=6bcd10bc4ada11a04bc2b7425afe5a8855592cd2;hpb=d5738d17b54186db8c9c7f119a03b58382ae9be4

diff --git a/ipc.c b/ipc.c
index c1069ad9..89bbe535 100644
--- a/ipc.c
+++ b/ipc.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2006-2011 Andre Noll <maan@systemlinux.org>
+ * Copyright (C) 2006-2013 Andre Noll <maan@systemlinux.org>
  *
  * Licensed under the GPL v2. For licencing details see COPYING.
  */
@@ -9,6 +9,10 @@
 #include "para.h"
 #include "error.h"
 #include "ipc.h"
+#include <sys/types.h>
+#include <sys/param.h>
+#include <sys/sysctl.h>
+
 #include <sys/ipc.h>
 #include <sys/shm.h>
 #include <sys/sem.h>
@@ -171,3 +175,55 @@ int shm_detach(void *addr)
 	int ret = shmdt(addr);
 	return ret < 0? -ERRNO_TO_PARA_ERROR(errno) : 1;
 }
+
+# if defined __FreeBSD__ || defined __NetBSD__
+# 	define SYSCTL_SHMMAX_VARIABLE "kern.ipc.shmmax"
+# elif defined __APPLE__
+# 	define SYSCTL_SHMMAX_VARIABLE "kern.sysv.shmmax"
+# else
+#	undef SYSCTL_SHMMAX_VARIABLE
+# endif
+
+/**
+ * Get the maximal size of a shared memory area.
+ *
+ * The value is only computed once when the function is called for the first
+ * time.  Subsequent calls return the number which was computed during the
+ * first call.
+ *
+ * \return A number suitable as an argument to \ref shm_new().
+ */
+size_t shm_get_shmmax(void)
+{
+	static size_t shmmax;
+
+	if (shmmax > 0) /* only dance once */
+		return shmmax;
+#ifdef __linux__ /* get it from proc fs */
+	{
+		int fd = open("/proc/sys/kernel/shmmax", O_RDONLY);
+		if (fd >= 0) {
+			char buf[100] = "";
+			int ret = read(fd, buf, sizeof(buf) - 1);
+			if (ret > 0) {
+				buf[ret] = '\0';
+				shmmax = strtoul(buf, NULL, 10);
+			}
+			close(fd);
+		}
+	}
+#elif defined SYSCTL_SHMMAX_VARIABLE
+	{
+		size_t len = sizeof(shmmax);
+		sysctlbyname(SYSCTL_SHMMAX_VARIABLE, &shmmax, &len, NULL, 0);
+	}
+#elif defined SHMMAX
+	shmmax = SHMMAX;
+#endif
+	if (shmmax == 0) {
+		PARA_WARNING_LOG("unable to determine shmmax\n");
+		shmmax = 65535; /* last resort */
+	}
+	PARA_INFO_LOG("shmmax: %zu\n", shmmax);
+	return shmmax;
+}