Add a feature_present(3) function which checks to see if a named kernel

feature is present by checking the kern.features sysctl MIB.

MFC after:	1 week

1 files changed, 62 insertions, 0 deletions

diff --git a/lib/libc/gen/feature_present.c b/lib/libc/gen/feature_present.c
new file mode 100644
index 0000000..7a2c282
--- /dev/null
+++ b/lib/libc/gen/feature_present.c
@@ -0,0 +1,62 @@
+/*-
+ * Copyright (c) 2008 Yahoo!, Inc.
+ * All rights reserved.
+ * Written by: John Baldwin <jhb@FreeBSD.org>
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the author nor the names of any co-contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/types.h>
+#include <sys/sysctl.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+/*
+ * Returns true if the named feature is present in the currently
+ * running kernel.  A feature's presence is indicated by an integer
+ * sysctl node called kern.feature.<feature> that is non-zero.
+ */
+int
+feature_present(const char *feature)
+{
+	char *mib;
+	size_t len;
+	int i;
+
+	if (asprintf(&mib, "kern.features.%s", feature) < 0)
+		return (0);
+	len = sizeof(i);
+	if (sysctlbyname(mib, &i, &len, NULL, 0) < 0) {
+		free(mib);
+		return (0);
+	}
+	free(mib);
+	if (len != sizeof(i))
+		return (0);
+	return (i != 0);
+}