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-rw-r--r--toys/other/switch_root.c97
1 files changed, 97 insertions, 0 deletions
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);
+}