Lots of hacking:

- Turn Keyboard into a CharacterDevice (85,1) at /dev/keyboard.
- Implement MM::unmapRegionsForTask() and MM::unmapRegion()
- Save SS correctly on interrupt.
- Add a simple Spawn syscall for launching another process.
- Move a bunch of IO syscall debug output behind DEBUG_IO.
- Have ASSERT do a "cli" immediately when failing.
  This makes the output look proper every time.
- Implement a bunch of syscalls in LibC.
- Add a simple shell ("sh"). All it can do now is read a line
  of text from /dev/keyboard and then try launching the specified
  executable by calling spawn().

There are definitely bugs in here, but we're moving on forward.

Userland/sh.cpp

@@ -0,0 +1,56 @@
+#include <LibC/stdio.h>
+#include <LibC/unistd.h>
+#include <LibC/process.h>
+
+static void prompt()
+{
+    if (getuid() == 0)
+        printf("# ");
+    else
+        printf("$ ");
+}
+
+static int runcmd(char* cmd)
+{
+    //printf("command: '%s'\n", cmd);
+    int ret = spawn(cmd);
+    if (ret == -1) {
+        printf("spawn failed: %s\n", cmd);
+    }
+    return 0;
+}
+
+int main(int c, char** v)
+{
+    char linebuf[128];
+    int linedx = 0;
+    linebuf[0] = '\0';
+
+    int fd = open("/dev/keyboard");
+    if (fd == -1) {
+        printf("failed to open /dev/keyboard :(\n");
+        return 1;
+    }
+    prompt();
+    for (;;) {
+        char keybuf[16];
+        ssize_t nread = read(fd, keybuf, sizeof(keybuf));
+        if (nread < 0) {
+            printf("failed to read :(\n");
+            return 2;
+        }
+        for (ssize_t i = 0; i < nread; ++i) {
+            putchar(keybuf[i]);
+            if (keybuf[i] != '\n') {
+                linebuf[linedx++] = keybuf[i];
+                linebuf[linedx] = '\0';
+            } else {
+                runcmd(linebuf);
+                linebuf[0] = '\0';
+                linedx = 0;
+                prompt();
+            }
+        }
+    }
+    return 0;
+}