Add the function sysctlnametomib to libc. Details on the semantics

and use of this function have been added to the sysctl.3 manual page.

3 files changed, 111 insertions, 3 deletions

diff --git a/lib/libc/gen/Makefile.inc b/lib/libc/gen/Makefile.inc
index 37d5a0d..afe8e91 100644
--- a/lib/libc/gen/Makefile.inc
+++ b/lib/libc/gen/Makefile.inc
@@ -25,7 +25,7 @@ SRCS+=  _rand48.c _spinlock_stub.c alarm.c arc4random.c assert.c \
 	setdomainname.c sethostname.c setjmperr.c setmode.c setproctitle.c \
 	shmat.c shmctl.c shmdt.c shmget.c siginterrupt.c siglist.c signal.c \
 	sigsetops.c sleep.c srand48.c stringlist.c strtofflags.c \
-	sysconf.c sysctl.c sysctlbyname.c \
+	sysconf.c sysctl.c sysctlbyname.c sysctlnametomib.c \
 	syslog.c telldir.c termios.c time.c times.c timezone.c ttyname.c \
 	ttyslot.c ualarm.c uname.c unvis.c usleep.c utime.c valloc.c vis.c \
 	wait.c wait3.c waitpid.c
@@ -115,7 +115,7 @@ MLINKS+=sigsetops.3 sigaddset.3 sigsetops.3 sigdelset.3 \
 	sigsetops.3 sigismember.3
 MLINKS+=stringlist.3 sl_add.3 stringlist.3 sl_find.3 \
 	stringlist.3 sl_free.3 stringlist.3 sl_init.3
-MLINKS+=sysctl.3 sysctlbyname.3
+MLINKS+=sysctl.3 sysctlbyname.3 sysctl.3 sysctlnametomib.3
 MLINKS+=syslog.3 closelog.3 syslog.3 openlog.3 syslog.3 setlogmask.3 \
 	syslog.3 vsyslog.3
 MLINKS+=tcsendbreak.3 tcdrain.3 tcsendbreak.3 tcflow.3 tcsendbreak.3 tcflush.3
diff --git a/lib/libc/gen/sysctl.3 b/lib/libc/gen/sysctl.3
index b67d603..2470c0e 100644
--- a/lib/libc/gen/sysctl.3
+++ b/lib/libc/gen/sysctl.3
@@ -37,7 +37,8 @@
 .Os
 .Sh NAME
 .Nm sysctl ,
-.Nm sysctlbyname
+.Nm sysctlbyname ,
+.Nm sysctlnametomib
 .Nd get or set system information
 .Sh LIBRARY
 .Lb libc
@@ -48,6 +49,8 @@
 .Fn sysctl "int *name" "u_int namelen" "void *oldp" "size_t *oldlenp" "void *newp" "size_t newlen"
 .Ft int
 .Fn sysctlbyname "const char *name" "void *oldp" "size_t *oldlenp" "void *newp" "size_t newlen"
+.Ft int
+.Fn sysctlnametomib "const char *name" "int *mibp" "size_t *sizep"
 .Sh DESCRIPTION
 The
 .Fn sysctl
@@ -126,6 +129,56 @@ should be set to NULL and
 .Fa newlen
 set to 0.
 .Pp
+The
+.Fn sysctlnametomib
+function accepts an ASCII representation of the name,
+looks up the integer name vector,
+and returns the numeric representation in the mib array pointed to by
+.Fa mibp .
+The number of elements in the mib array is given by the location specified by
+.Fa sizep
+before the call,
+and that location gives the number of entries copied after a successful call.
+The resulting
+.Fa mib
+and
+.Fa size
+may be used in subsequent
+.Fn sysctl
+calls to get the data associated with the requested ASCII name.
+This interface is intended for use by applications that want to
+repeatedly request the same variable (the
+.Fn sysctl
+function runs in about a third the time as the same request made via the
+.Fn sysctlbyname
+function).
+The
+.Fn sysctlbyname
+function is also useful for fetching mib prefixes and then adding
+a final component.
+For example, to fetch process information
+for processes with pid's less than 100:
+
+.Bd -literal -offset indent -compact
+int i, mib[4];
+size_t len;
+struct kinfo_proc kp;
+
+/* Fill out the first three components of the mib */
+len = 4;
+sysctlnametomib("kern.proc.pid", mib, &len);
+
+/* Fetch and print entries for pid's < 100 */
+for (i = 0; i < 100; i++) {
+	mib[3] = i;
+	len = sizeof(kp);
+	if (sysctl(mib, 4, &kp, &len, NULL, 0) == -1)
+		perror("sysctl");
+	else if (len > 0)
+		printkproc(&kp);
+}
+.Ed
+.Pp
 The top level names are defined with a CTL_ prefix in
 .Aq Pa sys/sysctl.h ,
 and are as follows.
diff --git a/lib/libc/gen/sysctlnametomib.c b/lib/libc/gen/sysctlnametomib.c
new file mode 100644
index 0000000..4cfa5c2
--- /dev/null
+++ b/lib/libc/gen/sysctlnametomib.c
@@ -0,0 +1,55 @@
+/*
+ * Copyright 2001 The FreeBSD Project. All Rights Reserved.
+ *
+ * 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.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE FREEBSD PROJECT ``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 FREEBSD PROJECT 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.
+ *
+ * $FreeBSD$
+ */
+
+#include <sys/types.h>
+#include <sys/sysctl.h>
+
+/*
+ * This function uses a presently undocumented interface to the kernel
+ * to walk the tree and get the type so it can print the value.
+ * This interface is under work and consideration, and should probably
+ * be killed with a big axe by the first person who can find the time.
+ * (be aware though, that the proper interface isn't as obvious as it
+ * may seem, there are various conflicting requirements.
+ */
+int
+sysctlnametomib(const char *name, int *mibp, size_t *sizep)
+{
+	int oid[2];
+	int error;
+
+	oid[0] = 0;
+	oid[1] = 3;
+
+	*sizep *= sizeof (int);
+	error = sysctl(oid, 2, mibp, sizep, name, strlen(name));
+	*sizep /= sizeof (int);
+	if (error < 0) 
+		return (error);
+	return (0);
+}