Add srandomdev() description

lib/libc/stdlib/random.3

@@ -37,6 +37,7 @@
 .Sh NAME
 .Nm random ,
 .Nm srandom ,
+.Nm srandomdev ,
 .Nm initstate ,
 .Nm setstate
 .Nd better random number generator; routines for changing generators
@@ -46,6 +47,8 @@
 .Fn random void
 .Ft void
 .Fn srandom "unsigned long seed"
+.Ft int
+.Fn srandomdev void
 .Ft char *
 .Fn initstate "unsigned long seed" "char *state" "long n"
 .Ft char *
@@ -93,6 +96,25 @@ with
 as the seed.
 .Pp
 The
+.Fn srandomdev
+routine initialize a state array using
+.Xr urandom 4
+random number device which returns good random numbers,
+suitable for cryptographic use.
+Note that this particular seeding
+procedure can generate states which are impossible to reproduce by
+calling
+.Fn srandom
+with any value, since the succeeding terms in the
+state buffer are no longer derived from the LC algorithm applied to
+a fixed seed.
+If successful
+.Fn srandomdev
+returns 0. It returns -1 on failure, and sets
+.Va errno
+to indicate the error.
+.Pp
+The
 .Fn initstate
 routine allows a state array, passed in as an argument, to be initialized
 for future use.  The size of the state array (in bytes) is used by
@@ -155,7 +177,8 @@ detects that the state information has been garbled, error
 messages are printed on the standard error output.
 .Sh SEE ALSO
 .Xr rand 3 ,
-.Xr srand 3
+.Xr srand 3 ,
+.Xr urandom 4
 .Sh HISTORY
 These
 functions appeared in