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

4 files changed, 138 insertions, 2 deletions

diff --git a/include/unistd.h b/include/unistd.h
index 48c925c340a0..51aa088486f2 100644
--- a/include/unistd.h
+++ b/include/unistd.h
@@ -480,6 +480,7 @@ int	 des_setkey(const char *key);
 void	 endusershell(void);
 int	 exect(const char *, char * const *, char * const *);
 int	 execvP(const char *, const char *, char * const *);
+int	 feature_present(const char *);
 char	*fflagstostr(u_long);
 int	 getdomainname(char *, int);
 int	 getgrouplist(const char *, gid_t, gid_t *, int *);
diff --git a/lib/libc/gen/Makefile.inc b/lib/libc/gen/Makefile.inc
index 8ea422d2d9f2..10c6ceb123fe 100644
--- a/lib/libc/gen/Makefile.inc
+++ b/lib/libc/gen/Makefile.inc
@@ -10,7 +10,7 @@ SRCS+=  __getosreldate.c __xuname.c \
 	clock.c closedir.c confstr.c \
 	crypt.c ctermid.c daemon.c devname.c dirname.c disklabel.c \
 	dlfcn.c dlfunc.c drand48.c erand48.c err.c errlst.c errno.c \
-	exec.c fmtcheck.c fmtmsg.c fnmatch.c \
+	exec.c feature_present.c fmtcheck.c fmtmsg.c fnmatch.c \
 	fpclassify.c frexp.c fstab.c ftok.c fts.c ftw.c \
 	getbootfile.c getbsize.c \
 	getcap.c getcwd.c getdomainname.c getgrent.c getgrouplist.c \
@@ -45,7 +45,8 @@ MAN+=	alarm.3 arc4random.3 \
 	basename.3 check_utility_compat.3 clock.3 \
 	confstr.3 ctermid.3 daemon.3 devname.3 directory.3 dirname.3 \
 	dladdr.3 dlinfo.3 dllockinit.3 dlopen.3 \
-	err.3 exec.3 fmtcheck.3 fmtmsg.3 fnmatch.3 fpclassify.3 frexp.3 \
+	err.3 exec.3 \
+	feature_present.3 fmtcheck.3 fmtmsg.3 fnmatch.3 fpclassify.3 frexp.3 \
 	ftok.3 fts.3 ftw.3 \
 	getbootfile.3 getbsize.3 getcap.3 getcontext.3 getcwd.3 \
 	getdiskbyname.3 getdomainname.3 getfsent.3 \
diff --git a/lib/libc/gen/feature_present.3 b/lib/libc/gen/feature_present.3
new file mode 100644
index 000000000000..9a4269e9c9af
--- /dev/null
+++ b/lib/libc/gen/feature_present.3
@@ -0,0 +1,72 @@
+.\" 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.
+.\"
+.\" $FreeBSD$
+.\"
+.Dd January 8, 2008
+.Dt feature_present 3
+.Os
+.Sh NAME
+.Nm feature_present
+.Nd query presence of a kernel feature
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In unistd.h
+.Ft int
+.Fn feature_present "const char *feature"
+.Sh DESCRIPTION
+The
+.Fn feature_present
+function provides a method for an application to determine if a specific
+kernel feature is present in the currently running kernel.
+The
+.Fa feature
+argument specifies the name of the feature to check.
+The
+.Fn feature_present
+function will return 1 if the specified feature is present,
+otherwise it will return 0.
+If the
+.Fn feature_present
+function is not able to determine the presence of
+.Fa feature
+due to an internal error it will return 0.
+.Sh RETURN VALUES
+If
+.Fa feature
+is present then 1 is returned;
+otherwise 0 is returned.
+.Sh SEE ALSO
+.Xr sysconf 3 ,
+.Xr sysctl 3
+.Sh HISTORY
+The
+.Fn feature_present
+function first appeared in
+.Fx 8.0 .
diff --git a/lib/libc/gen/feature_present.c b/lib/libc/gen/feature_present.c
new file mode 100644
index 000000000000..7a2c28265c3d
--- /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);
+}