first commit

user/init.c

@@ -0,0 +1,54 @@
+// init: The initial user-level program
+
+#include "kernel/types.h"
+#include "kernel/stat.h"
+#include "kernel/spinlock.h"
+#include "kernel/sleeplock.h"
+#include "kernel/fs.h"
+#include "kernel/file.h"
+#include "user/user.h"
+#include "kernel/fcntl.h"
+
+char *argv[] = { "sh", 0 };
+
+int
+main(void)
+{
+  int pid, wpid;
+
+  if(open("console", O_RDWR) < 0){
+    mknod("console", CONSOLE, 0);
+    open("console", O_RDWR);
+  }
+  dup(0);  // stdout
+  dup(0);  // stderr
+
+  for(;;){
+    printf("init: starting sh\n");
+    pid = fork();
+    if(pid < 0){
+      printf("init: fork failed\n");
+      exit(1);
+    }
+    if(pid == 0){
+      exec("sh", argv);
+      printf("init: exec sh failed\n");
+      exit(1);
+    }
+
+    for(;;){
+      // this call to wait() returns if the shell exits,
+      // or if a parentless process exits.
+      wpid = wait((int *) 0);
+      if(wpid == pid){
+        // the shell exited; restart it.
+        break;
+      } else if(wpid < 0){
+        printf("init: wait returned an error\n");
+        exit(1);
+      } else {
+        // it was a parentless process; do nothing.
+      }
+    }
+  }
+}