From 787eac5f1dac70ee4a6ac79699f6da87b8fd6ee6 Mon Sep 17 00:00:00 2001
From: Rob Landley <rob@landley.net>
Date: Sat, 8 Sep 2012 01:27:54 -0500
Subject: Add switch_root and fix infrastructure to understand name
 "switch_root".

---
 toys/other/switch_root.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 toys/other/switch_root.c

(limited to 'toys')

diff --git a/toys/other/switch_root.c b/toys/other/switch_root.c
new file mode 100644
index 00000000..b4c0b7dd
--- /dev/null
+++ b/toys/other/switch_root.c
@@ -0,0 +1,97 @@
+/* switch_root.c - Switch from rootfs/initramfs to another filesystem
+ *
+ * Copyright 2005 Rob Landley <rob@landley.net>
+
+USE_SWITCH_ROOT(NEWTOY(switch_root, "<2c:h", TOYFLAG_SBIN))
+
+config SWITCH_ROOT
+	bool "switch_root"
+	default y
+	help
+	  usage: switch_root [-c /dev/console] NEW_ROOT NEW_INIT...
+
+	  Use from PID 1 under initramfs to free initramfs, chroot to NEW_ROOT,
+	  and exec NEW_INIT.
+
+	  -c	Redirect console to device in NEW_ROOT
+	  -h	Hang instead of exiting on failure (avoids kernel panic)
+*/
+
+#include "toys.h"
+#include <sys/vfs.h>
+
+DEFINE_GLOBALS(
+   char *console;
+
+   dev_t rootdev;
+)
+
+#define TT this.switch_root
+
+#define FLAG_h  (1<<0)
+#define FLAG_c	(1<<1)
+
+static int del_node(struct dirtree *node)
+{
+   if (node->st.st_dev == TT.rootdev && dirtree_notdotdot(node)) {
+      int flag = 0;
+      if (S_ISDIR(node->st.st_mode)) {
+         if (node->data != -1) return DIRTREE_COMEAGAIN;
+         flag = AT_REMOVEDIR;
+      }
+      unlinkat(dirtree_parentfd(node), node->name, flag);
+   }
+
+   return 0;
+}
+
+void switch_root_main(void)
+{
+   char *newroot = *toys.optargs, **cmdline = toys.optargs+1;
+   struct stat st1, st2;
+   struct statfs stfs;
+   int console = console; // gcc's "may be used" warnings are broken.
+
+   if (getpid() != 1) error_exit("not pid 1");
+
+   // Root filesystem we're leaving must be ramfs or tmpfs
+   if (statfs("/", &stfs) ||
+      (stfs.f_type != 0x858458f6 && stfs.f_type != 0x01021994))
+   {
+      error_msg("not ramfs");
+      goto panic;
+   }
+
+   // New directory must be different filesystem instance
+   if (chdir(newroot) || stat(".", &st1) || stat("/", &st2) ||
+      st1.st_dev == st2.st_dev)
+   {
+      error_msg("bad newroot '%s'", newroot);
+      goto panic;
+   }
+   TT.rootdev=st2.st_dev;
+
+   // init program must exist and be an executable file
+   if (stat("init", &st1) || !S_ISREG(st1.st_mode) || !(st1.st_mode&0100)) {
+      error_msg("bad init");
+      goto panic;
+   }
+
+   if (TT.console && -1 == (console = open(TT.console, O_RDWR))) {
+      perror_msg("bad console '%s'", TT.console);
+      goto panic;
+   }
+ 
+   // Ok, enough safety checks: wipe root partition.
+   dirtree_read("/", del_node);
+
+   if (TT.console) {
+      int i;
+      for (i=0; i<3; i++) if (console != i) dup2(console, i);
+      if (console>2) close(console);
+   }
+   execv(*cmdline, cmdline);
+   perror_msg("Failed to exec '%s'", *cmdline);
+panic:
+   if (toys.optflags & FLAG_h) for (;;) wait(NULL);
+}
-- 
cgit v1.2.3