Add a simple /dev/random.

Author: https://github.com/awesomekling
Commit: https://github.com/SerenityOS/serenity/commit/05b088ee2f0

VirtualFileSystem/Makefile

@@ -22,6 +22,7 @@ VFS_OBJS = \
     ZeroDevice.o \
     NullDevice.o \
     FullDevice.o \
+    RandomDevice.o \
     test.o
 
 OBJS = $(AK_OBJS) $(VFS_OBJS)

VirtualFileSystem/RandomDevice.cpp

@@ -0,0 +1,47 @@
+#include "RandomDevice.h"
+#include "Limits.h"
+#include <AK/StdLib.h>
+#include <cstring>
+#include <cstdio>
+
+RandomDevice::RandomDevice()
+{
+}
+
+RandomDevice::~RandomDevice()
+{
+}
+
+// Simple rand() and srand() borrowed from the POSIX standard:
+
+static unsigned long next = 1;
+
+#define MY_RAND_MAX 32767
+static int myrand()
+{
+    next = next * 1103515245 + 12345;
+    return((unsigned)(next/((MY_RAND_MAX + 1) * 2)) % (MY_RAND_MAX + 1));
+}
+
+static void mysrand(unsigned seed)
+{
+    next = seed;
+}
+
+Unix::ssize_t RandomDevice::read(byte* buffer, Unix::size_t bufferSize)
+{
+    const int range = 'z' - 'a';
+    Unix::ssize_t nread = min(bufferSize, GoodBufferSize);
+    for (Unix::ssize_t i = 0; i < nread; ++i) {
+        double r = ((double)myrand() / (double)MY_RAND_MAX) * (double)range;
+        buffer[i] = 'a' + r;
+    }
+    return nread;
+}
+
+Unix::ssize_t RandomDevice::write(const byte*, Unix::size_t bufferSize)
+{
+    // FIXME: Use input for entropy? I guess that could be a neat feature?
+    return min(GoodBufferSize, bufferSize);
+}
+

VirtualFileSystem/RandomDevice.h

@@ -0,0 +1,13 @@
+#pragma once
+
+#include "CharacterDevice.h"
+
+class RandomDevice final : public CharacterDevice {
+public:
+    RandomDevice();
+    virtual ~RandomDevice();
+
+    Unix::ssize_t read(byte* buffer, Unix::size_t bufferSize) override;
+    Unix::ssize_t write(const byte* buffer, Unix::size_t bufferSize) override;
+};
+

VirtualFileSystem/test.cpp

@@ -6,6 +6,7 @@
 #include "ZeroDevice.h"
 #include "NullDevice.h"
 #include "FullDevice.h"
+#include "RandomDevice.h"
 #include <cstring>
 #include <AK/SimpleMalloc.h>
 #include <AK/kmalloc.h>
@@ -29,6 +30,9 @@ int main(int c, char** v)
     auto full = make<FullDevice>();
     vfs.registerCharacterDevice(1, 7, *full);
 
+    auto random = make<RandomDevice>();
+    vfs.registerCharacterDevice(1, 8, *random);
+
     if (!vfs.mountRoot(makeFileSystem(filename))) {
         printf("Failed to mount root :(\n");
         return 1;
@@ -187,7 +191,6 @@ int main(int c, char** v)
             byte buffer[512];
             for (;;) {
                 nread = handle->read(buffer, sizeof(buffer));
-                printf("read() returned %d\n", nread);
                 if (nread <= 0)
                     break;
                 fwrite(buffer, 1, nread, stdout);