cpu/native: add high-quality random implementation

Per default random data is read from `/dev/random` now.

If specified (e.g. `-s 4711`), data is generated by calls to POSIX
random function like before. The POSIX random API is initialize with
the given seed (`srandom(4711);` in this example).

cpu/native/include/native_internal.h

@@ -145,6 +145,8 @@ extern const char *_progname;
 extern char **_native_argv;
 extern pid_t _native_pid;
 extern pid_t _native_id;
+extern unsigned _native_rng_seed;
+extern int _native_rng_mode; /**< 0 = /dev/random, 1 = random(3) */
 extern const char *_native_unix_socket_path;
 
 #ifdef MODULE_UART0

cpu/native/periph/random.c

@@ -8,6 +8,7 @@
 
 /**
  * @ingroup     native_cpu
+ * @defgroup    native_rng
  * @{
  *
  * @author      Ludwig Ortmann <ludwig.ortmann@fu-berlin.de>
@@ -16,6 +17,9 @@
 #include <string.h>
 #include <stdlib.h>
 #include <err.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
 
 #include "cpu-conf.h"
 #include "native_internal.h"
@@ -26,10 +30,40 @@
 #include "debug.h"
 
 static int powered = 0;
+static int dev_random = -1;
+
+/**********************************************************************
+ * internal API declaration
+ **********************************************************************/
+
+/**
+ * seed host random module with @ref _native_rng_seed
+ */
+void _native_rng_init_det(void);
+void _native_rng_init_hq(void);
+unsigned _native_rng_read_det(char *buf, unsigned num);
+unsigned _native_rng_read_hq(char *buf, unsigned num);
+
+/**********************************************************************
+ * public API implementation
+ **********************************************************************/
 
 void random_init(void)
 {
-    DEBUGF("random_init: powering on\n");
+    DEBUG("random_init: initializing\n");
+    switch (_native_rng_mode) {
+        case 0:
+            _native_rng_init_hq();
+            break;
+        case 1:
+            _native_rng_init_det();
+            break;
+        default:
+            err(EXIT_FAILURE, "random_init: _native_rng_mode is in invalid state %i\n",
+                   _native_rng_mode);
+            break;
+    }
+    DEBUG("random_init: powering on\n");
     random_poweron();
 }
 
@@ -40,31 +74,89 @@ int random_read(char *buf, unsigned int num)
         return 0;
     }
 
-    DEBUGF("random_read: writing %ui bytes\n", num);
+    DEBUG("random_read: writing %u bytes\n", num);
+    switch (_native_rng_mode) {
+        case 0:
+            num = _native_rng_read_hq(buf, num);
+            break;
+        case 1:
+            num = _native_rng_read_det(buf, num);
+            break;
+        default:
+            num = 0;
+            err(EXIT_FAILURE, "random_read: _native_rng_mode is in invalid state %i\n",
+                   _native_rng_mode);
+            break;
+    }
+    return num;
+}
+
+void random_poweron(void)
+{
+    DEBUG("random_poweron: power on\n");
+    powered = 1;
+}
+
+void random_poweroff(void)
+{
+    DEBUG("random_poweroff: power off\n");
+    powered = 0;
+}
+
+/**********************************************************************
+ * internal API implementation
+ **********************************************************************/
+
+void _native_rng_init_det(void)
+{
+    DEBUG("_native_rng_init_det\n");
+    _native_syscall_enter();
+    real_srandom(_native_rng_seed);
+    _native_syscall_leave();
+}
+
+void _native_rng_init_hq(void)
+{
+    DEBUG("_native_rng_init_hq\n");
+    _native_syscall_enter();
+    dev_random = real_open("/dev/random", O_RDONLY);
+    if (dev_random == -1) {
+        err(EXIT_FAILURE, "_native_rng_init_hq: open(/dev/random)");
+    }
+    _native_syscall_leave();
+}
+
+unsigned _native_rng_read_det(char *buf, unsigned num)
+{
+    DEBUG("_native_rng_read_det\n");
     for (unsigned i = 0; i < num; i++) {
         _native_syscall_enter();
         buf[i] = (char)real_random();
         _native_syscall_leave();
     }
+
     return num;
 }
 
-/**
- * seed host random module with @ref _native_id
- */
-void random_poweron(void)
+unsigned _native_rng_read_hq(char *buf, unsigned num)
 {
-    DEBUGF("random_poweron: power on\n");
-    powered = 1;
-    _native_syscall_enter();
-    real_srandom((unsigned int)_native_id);
-    _native_syscall_leave();
-}
+    DEBUG("_native_rng_read_hq\n");
+    unsigned offset = 0;
 
-void random_poweroff(void)
-{
-    DEBUGF("random_poweroff: power off\n");
-    powered = 0;
+    while (num > 0) {
+        _native_syscall_enter();
+        int r = real_read(dev_random, (buf + offset), num);
+        _native_syscall_leave();
+
+        if (r == -1) {
+            err(EXIT_FAILURE, "_native_rng_read_hq: read");
+        }
+
+        num -= r;
+        offset += r;
+    }
+
+    return offset;
 }
 
 /**

cpu/native/startup.c

@@ -43,6 +43,8 @@ const char *_progname;
 char **_native_argv;
 pid_t _native_pid;
 pid_t _native_id;
+unsigned _native_rng_seed = 0;
+int _native_rng_mode = 0;
 const char *_native_unix_socket_path = NULL;
 
 /**
@@ -202,6 +204,8 @@ void usage_exit(void)
 #endif
     real_printf("\
 -i <id>     specify instance id (set by config module)\n\
+-s <seed>   specify srandom(3) seed (/dev/random is used instead of\n\
+            random(3) if the option is omitted)\n\
 -d          daemonize\n\
 -e          redirect stderr to file\n\
 -E          do not redirect stderr (i.e. leave sterr unchanged despite\n\
@@ -262,6 +266,16 @@ __attribute__((constructor)) static void startup(int argc, char **argv)
             }
             _native_id = atol(argv[argp]);
         }
+        else if (strcmp("-s", arg) == 0) {
+            if (argp + 1 < argc) {
+                argp++;
+            }
+            else {
+                usage_exit();
+            }
+            _native_rng_seed = atol(argv[argp]);
+            _native_rng_mode = 1;
+        }
         else if (strcmp("-d", arg) == 0) {
             if (strcmp(stdiotype, "stdio") == 0) {
                 stdiotype = "null";