random(9): Deprecate random(9), remove meaningless srandom(9)

srandom(9) is meaningless on SMP systems or any system with, say,
interrupts.  One could never rely on random(9) to produce a reproducible
sequence of outputs on the basis of a specific srandom() seed because the
global state was shared by all kernel contexts.  As such, removing it is
literally indistinguishable to random(9) consumers (as compared with
retaining it).

Mark random(9) as deprecated and slated for quick removal.  This is not to
say we intend to remove all fast, non-cryptographic PRNG(s) in the kernel.
It/they just won't be random(9), as it exists today, in either name or
implementation.

Before random(9) is removed, a replacement will be provided and in-tree
consumers will be converted.

Note that despite the name, the random(9) interface does not bear any
resemblance to random(3).  Instead, it is the same crummy 1988 Park-Miller
LCG used in libc rand(3).

1 files changed, 12 insertions, 13 deletions

diff --git a/sys/libkern/random.c b/sys/libkern/random.c
index 5f2651130ab7..e5e9de6108e1 100644
--- a/sys/libkern/random.c
+++ b/sys/libkern/random.c
@@ -34,32 +34,31 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include <sys/types.h>
 #include <sys/libkern.h>
-
-#define NSHUFF 50       /* to drop some "seed -> 1st value" linearity */
+#include <sys/systm.h>
 
 static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
 
-void
-srandom(u_long seed)
-{
-	int i;
-
-	randseed = seed;
-	for (i = 0; i < NSHUFF; i++)
-		(void)random();
-}
-
 /*
  * Pseudo-random number generator for perturbing the profiling clock,
  * and whatever else we might use it for.  The result is uniform on
  * [0, 2^31 - 1].
  */
 u_long
-random()
+random(void)
 {
+	static bool warned = false;
+
 	long x, hi, lo, t;
 
+	/* Warn only once, or it gets very spammy. */
+	if (!warned) {
+		gone_in(13,
+		    "random(9) is the obsolete Park-Miller LCG from 1988");
+		warned = true;
+	}
+
 	/*
 	 * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
 	 * From "Random number generators: good ones are hard to find",