1) example (partially humorous random_adaptor, that I call "EXAMPLE")

 * It's not meant to be used in a real system, it's there to show how
   the basics of how to create interfaces for random_adaptors. Perhaps
   it should belong in a manual page

2) Move probe.c's functionality in to random_adaptors.c
 * rename random_ident_hardware() to random_adaptor_choose()

3) Introduce a new way to choose (or select) random_adaptors via tunable
"rngs_want" It's a list of comma separated names of adaptors, ordered
by preferences. I.e.:
rngs_want="yarrow,rdrand"

Such setting would cause yarrow to be preferred to rdrand. If neither of
them are available (or registered), then system will default to
something reasonable (currently yarrow). If yarrow is not present, then
we fall back to the adaptor that's first on the list of registered
adaptors.

4) Introduce a way where RNGs can play a role of entropy source. This is
mostly useful for HW rngs.

The way I envision this is that every HW RNG will use this
functionality by default. Functionality to disable this is also present.
I have an example of how to use this in random_adaptor_example.c (see
modload event, and init function)

5) fix kern.random.adaptors from
kern.random.adaptors: yarrowpanicblock
to
kern.random.adaptors: yarrow,panic,block

6) add kern.random.active_adaptor to indicate currently selected
adaptor:
root@freebsd04:~ # sysctl kern.random.active_adaptor
kern.random.active_adaptor: yarrow

Submitted by:	Arthur Mesh <arthurmesh@gmail.com>

3 files changed, 119 insertions, 1 deletions

diff --git a/share/examples/kld/Makefile b/share/examples/kld/Makefile
index 4e3b641..5e6fc74 100644
--- a/share/examples/kld/Makefile
+++ b/share/examples/kld/Makefile
@@ -67,6 +67,6 @@
 #	$FreeBSD$
 #
 
-SUBDIR=	cdev dyn_sysctl firmware khelp syscall
+SUBDIR=	cdev dyn_sysctl firmware khelp random_adaptor syscall
 
 .include <bsd.subdir.mk>
diff --git a/share/examples/kld/random_adaptor/Makefile b/share/examples/kld/random_adaptor/Makefile
new file mode 100644
index 0000000..d19b4dc
--- /dev/null
+++ b/share/examples/kld/random_adaptor/Makefile
@@ -0,0 +1,6 @@
+# $FreeBSD$
+
+KMOD=  random_adaptor_example
+SRCS=  ${KMOD}.c
+
+.include <bsd.kmod.mk>
diff --git a/share/examples/kld/random_adaptor/random_adaptor_example.c b/share/examples/kld/random_adaptor/random_adaptor_example.c
new file mode 100644
index 0000000..f94a7c2
--- /dev/null
+++ b/share/examples/kld/random_adaptor/random_adaptor_example.c
@@ -0,0 +1,112 @@
+/*-
+ * Copyright (c) 2013 Arthur Mesh <arthurmesh@gmail.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer
+ *    in this position and unchanged.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/kernel.h>
+#include <sys/module.h>
+#include <sys/selinfo.h>
+#include <sys/systm.h>
+
+#include <dev/random/random_adaptors.h>
+#include <dev/random/randomdev.h>
+
+static int random_example_entropy_control;
+
+#define RNG_NAME "example"
+
+static int random_example_read(void *, int);
+static void random_example_init(void);
+
+struct random_adaptor random_example = {
+	.ident = "Example RNG",
+	.init = random_example_init,
+	.deinit = (random_deinit_func_t *)random_null_func,
+	.read = random_example_read,
+	.write = (random_write_func_t *)random_null_func,
+	.reseed = (random_reseed_func_t *)random_null_func,
+	.seeded = 1,
+};
+
+static void
+random_example_init(void)
+{
+
+	/*
+	 * Init() is called only if this RNG was chosen to plugin in to
+	 * random(4). In which case, we should no longer use this adaptor as
+	 * an entropy source.
+	 */
+	random_example_entropy_control = 1;
+}
+
+/*
+ * Used under the license provided @ http://xkcd.com/221/
+ * http://creativecommons.org/licenses/by-nc/2.5/
+ */
+static u_char
+getRandomNumber(void)
+{
+	return 4;   /* chosen by fair dice roll, guaranteed to be random */
+}
+
+static int
+random_example_read(void *buf, int c)
+{
+	u_char *b;
+	int count;
+
+	b = buf;
+
+	for (count = 0; count < c; count++) {
+		b[count] = getRandomNumber();
+	}
+
+	printf("returning %d bytes of pure randomness\n", c);
+	return (c);
+}
+
+static int
+random_example_modevent(module_t mod, int type, void *unused)
+{
+
+	switch (type) {
+	case MOD_LOAD:
+		/* start off by using this as an entropy source */
+		random_adaptor_use_as_entropy(RNG_NAME, &random_example,
+		    &random_example_entropy_control);
+		random_adaptor_register(RNG_NAME, &random_example);
+		EVENTHANDLER_INVOKE(random_adaptor_attach, &random_example);
+		return (0);
+	}
+
+	return (EINVAL);
+}
+
+RANDOM_ADAPTOR_MODULE(random_example, random_example_modevent, 1);